<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux.git/arch/powerpc/include, branch v3.2-rc7</title>
<subtitle>Linux kernel source tree</subtitle>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/'/>
<entry>
<title>Merge branch 'kvm-updates/3.2' of git://git.kernel.org/pub/scm/virt/kvm/kvm</title>
<updated>2011-11-20T22:57:43+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2011-11-20T22:57:43+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=a4cc3889f7e2c3f2fd15b492822c889fed5e1800'/>
<id>a4cc3889f7e2c3f2fd15b492822c889fed5e1800</id>
<content type='text'>
* 'kvm-updates/3.2' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM guest: prevent tracing recursion with kvmclock
  Revert "KVM: PPC: Add support for explicit HIOR setting"
  KVM: VMX: Check for automatic switch msr table overflow
  KVM: VMX: Add support for guest/host-only profiling
  KVM: VMX: add support for switching of PERF_GLOBAL_CTRL
  KVM: s390: announce SYNC_MMU
  KVM: s390: Fix tprot locking
  KVM: s390: handle SIGP sense running intercepts
  KVM: s390: Fix RUNNING flag misinterpretation
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
* 'kvm-updates/3.2' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM guest: prevent tracing recursion with kvmclock
  Revert "KVM: PPC: Add support for explicit HIOR setting"
  KVM: VMX: Check for automatic switch msr table overflow
  KVM: VMX: Add support for guest/host-only profiling
  KVM: VMX: add support for switching of PERF_GLOBAL_CTRL
  KVM: s390: announce SYNC_MMU
  KVM: s390: Fix tprot locking
  KVM: s390: handle SIGP sense running intercepts
  KVM: s390: Fix RUNNING flag misinterpretation
</pre>
</div>
</content>
</entry>
<entry>
<title>Revert "KVM: PPC: Add support for explicit HIOR setting"</title>
<updated>2011-11-17T14:30:25+00:00</updated>
<author>
<name>Alexander Graf</name>
<email>agraf@suse.de</email>
</author>
<published>2011-11-17T14:26:35+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=bb75c627fb0dfb8c0ab75d3033709ff928896e16'/>
<id>bb75c627fb0dfb8c0ab75d3033709ff928896e16</id>
<content type='text'>
This reverts commit a15bd354f083f20f257db450488db52ac27df439.

It exceeded the padding on the SREGS struct, rendering the ABI
backwards-incompatible.

Conflicts:

	arch/powerpc/kvm/powerpc.c
	include/linux/kvm.h

Signed-off-by: Avi Kivity &lt;avi@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
This reverts commit a15bd354f083f20f257db450488db52ac27df439.

It exceeded the padding on the SREGS struct, rendering the ABI
backwards-incompatible.

Conflicts:

	arch/powerpc/kvm/powerpc.c
	include/linux/kvm.h

Signed-off-by: Avi Kivity &lt;avi@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc: Fix atomic_xxx_return barrier semantics</title>
<updated>2011-11-17T05:26:07+00:00</updated>
<author>
<name>Benjamin Herrenschmidt</name>
<email>benh@kernel.crashing.org</email>
</author>
<published>2011-11-15T17:11:27+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=b97021f85517552ea8a0d2c1680c1ee4beab6d14'/>
<id>b97021f85517552ea8a0d2c1680c1ee4beab6d14</id>
<content type='text'>
The Documentation/memory-barriers.txt document requires that atomic
operations that return a value act as a memory barrier both before
and after the actual atomic operation.

Our current implementation doesn't guarantee this. More specifically,
while a load following the isync can not be issued before stwcx. has
completed, that completion doesn't architecturally means that the
result of stwcx. is visible to other processors (or any previous stores
for that matter) (typically, the other processors L1 caches can still
hold the old value).

This has caused an actual crash in RCU torture testing on Power 7

This fixes it by changing those atomic ops to use new macros instead
of RELEASE/ACQUIRE barriers, called ATOMIC_ENTRY and ATMOIC_EXIT barriers,
which are then defined respectively to lwsync and sync.

I haven't had a chance to measure the performance impact (or rather
what I measured with kernel compiles is in the noise, I yet have to
find a more precise benchmark)

Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Acked-by: Paul E. McKenney &lt;paulmck@linux.vnet.ibm.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
The Documentation/memory-barriers.txt document requires that atomic
operations that return a value act as a memory barrier both before
and after the actual atomic operation.

Our current implementation doesn't guarantee this. More specifically,
while a load following the isync can not be issued before stwcx. has
completed, that completion doesn't architecturally means that the
result of stwcx. is visible to other processors (or any previous stores
for that matter) (typically, the other processors L1 caches can still
hold the old value).

This has caused an actual crash in RCU torture testing on Power 7

This fixes it by changing those atomic ops to use new macros instead
of RELEASE/ACQUIRE barriers, called ATOMIC_ENTRY and ATMOIC_EXIT barriers,
which are then defined respectively to lwsync and sync.

I haven't had a chance to measure the performance impact (or rather
what I measured with kernel compiles is in the noise, I yet have to
find a more precise benchmark)

Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Acked-by: Paul E. McKenney &lt;paulmck@linux.vnet.ibm.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc/book3e-64: Fix debug support for userspace</title>
<updated>2011-11-17T05:26:07+00:00</updated>
<author>
<name>Kumar Gala</name>
<email>galak@kernel.crashing.org</email>
</author>
<published>2011-10-06T02:53:40+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=187b9f2aa769198daa7cf8054abb65a08b8d8b47'/>
<id>187b9f2aa769198daa7cf8054abb65a08b8d8b47</id>
<content type='text'>
With the introduction of CONFIG_PPC_ADV_DEBUG_REGS user space debug is
broken on Book-E 64-bit parts that support delayed debug events.  When
switch_booke_debug_regs() sets DBCR0 we'll start getting debug events as
MSR_DE is also set and we aren't able to handle debug events from kernel
space.

We can remove the hack that always enables MSR_DE and loads up DBCR0 and
just utilize switch_booke_debug_regs() to get user space debug working
again.

We still need to handle critical/debug exception stacks &amp; proper
save/restore of state for those exception levles to support debug events
from kernel space like we have on 32-bit.

Signed-off-by: Kumar Gala &lt;galak@kernel.crashing.org&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
With the introduction of CONFIG_PPC_ADV_DEBUG_REGS user space debug is
broken on Book-E 64-bit parts that support delayed debug events.  When
switch_booke_debug_regs() sets DBCR0 we'll start getting debug events as
MSR_DE is also set and we aren't able to handle debug events from kernel
space.

We can remove the hack that always enables MSR_DE and loads up DBCR0 and
just utilize switch_booke_debug_regs() to get user space debug working
again.

We still need to handle critical/debug exception stacks &amp; proper
save/restore of state for those exception levles to support debug events
from kernel space like we have on 32-bit.

Signed-off-by: Kumar Gala &lt;galak@kernel.crashing.org&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc: Copy down exception vectors after feature fixups</title>
<updated>2011-11-16T03:47:54+00:00</updated>
<author>
<name>Anton Blanchard</name>
<email>anton@samba.org</email>
</author>
<published>2011-11-14T12:54:47+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=d715e433b7ad19c02fc4becf0d5e9a59f97925de'/>
<id>d715e433b7ad19c02fc4becf0d5e9a59f97925de</id>
<content type='text'>
kdump fails because we try to execute an HV only instruction. Feature
fixups are being applied after we copy the exception vectors down to 0
so they miss out on any updates.

We have always had this issue but it only became critical in v3.0
when we added CFAR support (breaks POWER5) and v3.1 when we added
POWERNV (breaks everyone).

Signed-off-by: Anton Blanchard &lt;anton@samba.org&gt;
Cc: &lt;stable@kernel.org&gt; [v3.0+]
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
kdump fails because we try to execute an HV only instruction. Feature
fixups are being applied after we copy the exception vectors down to 0
so they miss out on any updates.

We have always had this issue but it only became critical in v3.0
when we added CFAR support (breaks POWER5) and v3.1 when we added
POWERNV (breaks everyone).

Signed-off-by: Anton Blanchard &lt;anton@samba.org&gt;
Cc: &lt;stable@kernel.org&gt; [v3.0+]
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc/ps3: Fix lv1_gpu_attribute hcall</title>
<updated>2011-11-08T03:51:59+00:00</updated>
<author>
<name>Geoff Levand</name>
<email>geoff@infradead.org</email>
</author>
<published>2011-10-12T08:42:13+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=9fce85f7ff94f1a877c15ad3d6ffbaed4b5cd1a6'/>
<id>9fce85f7ff94f1a877c15ad3d6ffbaed4b5cd1a6</id>
<content type='text'>
The lv1_gpu_attribute hcall takes three, not five input
arguments.  Adjust the lv1 hcall table and all calls.

Signed-off-by: Geoff Levand &lt;geoff@infradead.org&gt;
CC: Takashi Iwai &lt;tiwai@suse.de&gt;
Acked-by: Takashi Iwai &lt;tiwai@suse.de&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
The lv1_gpu_attribute hcall takes three, not five input
arguments.  Adjust the lv1 hcall table and all calls.

Signed-off-by: Geoff Levand &lt;geoff@infradead.org&gt;
CC: Takashi Iwai &lt;tiwai@suse.de&gt;
Acked-by: Takashi Iwai &lt;tiwai@suse.de&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc/irq: Remove IRQF_DISABLED</title>
<updated>2011-11-08T03:51:46+00:00</updated>
<author>
<name>Yong Zhang</name>
<email>yong.zhang0@gmail.com</email>
</author>
<published>2011-10-21T23:56:27+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=a3a9f3b47d12b5f6dfc9c7ed9d7b193d77812195'/>
<id>a3a9f3b47d12b5f6dfc9c7ed9d7b193d77812195</id>
<content type='text'>
Since commit [e58aa3d2: genirq: Run irq handlers with interrupts disabled],
We run all interrupt handlers with interrupts disabled
and we even check and yell when an interrupt handler
returns with interrupts enabled (see commit [b738a50a:
genirq: Warn when handler enables interrupts]).

So now this flag is a NOOP and can be removed.

Signed-off-by: Yong Zhang &lt;yong.zhang0@gmail.com&gt;
Acked-by: Arnd Bergmann &lt;arnd@arndb.de&gt;
Acked-by: Geoff Levand &lt;geoff@infradead.org&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Since commit [e58aa3d2: genirq: Run irq handlers with interrupts disabled],
We run all interrupt handlers with interrupts disabled
and we even check and yell when an interrupt handler
returns with interrupts enabled (see commit [b738a50a:
genirq: Warn when handler enables interrupts]).

So now this flag is a NOOP and can be removed.

Signed-off-by: Yong Zhang &lt;yong.zhang0@gmail.com&gt;
Acked-by: Arnd Bergmann &lt;arnd@arndb.de&gt;
Acked-by: Geoff Levand &lt;geoff@infradead.org&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>Merge branch 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux</title>
<updated>2011-11-07T03:44:47+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2011-11-07T03:44:47+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=32aaeffbd4a7457bf2f7448b33b5946ff2a960eb'/>
<id>32aaeffbd4a7457bf2f7448b33b5946ff2a960eb</id>
<content type='text'>
* 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux: (230 commits)
  Revert "tracing: Include module.h in define_trace.h"
  irq: don't put module.h into irq.h for tracking irqgen modules.
  bluetooth: macroize two small inlines to avoid module.h
  ip_vs.h: fix implicit use of module_get/module_put from module.h
  nf_conntrack.h: fix up fallout from implicit moduleparam.h presence
  include: replace linux/module.h with "struct module" wherever possible
  include: convert various register fcns to macros to avoid include chaining
  crypto.h: remove unused crypto_tfm_alg_modname() inline
  uwb.h: fix implicit use of asm/page.h for PAGE_SIZE
  pm_runtime.h: explicitly requires notifier.h
  linux/dmaengine.h: fix implicit use of bitmap.h and asm/page.h
  miscdevice.h: fix up implicit use of lists and types
  stop_machine.h: fix implicit use of smp.h for smp_processor_id
  of: fix implicit use of errno.h in include/linux/of.h
  of_platform.h: delete needless include &lt;linux/module.h&gt;
  acpi: remove module.h include from platform/aclinux.h
  miscdevice.h: delete unnecessary inclusion of module.h
  device_cgroup.h: delete needless include &lt;linux/module.h&gt;
  net: sch_generic remove redundant use of &lt;linux/module.h&gt;
  net: inet_timewait_sock doesnt need &lt;linux/module.h&gt;
  ...

Fix up trivial conflicts (other header files, and  removal of the ab3550 mfd driver) in
 - drivers/media/dvb/frontends/dibx000_common.c
 - drivers/media/video/{mt9m111.c,ov6650.c}
 - drivers/mfd/ab3550-core.c
 - include/linux/dmaengine.h
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
* 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux: (230 commits)
  Revert "tracing: Include module.h in define_trace.h"
  irq: don't put module.h into irq.h for tracking irqgen modules.
  bluetooth: macroize two small inlines to avoid module.h
  ip_vs.h: fix implicit use of module_get/module_put from module.h
  nf_conntrack.h: fix up fallout from implicit moduleparam.h presence
  include: replace linux/module.h with "struct module" wherever possible
  include: convert various register fcns to macros to avoid include chaining
  crypto.h: remove unused crypto_tfm_alg_modname() inline
  uwb.h: fix implicit use of asm/page.h for PAGE_SIZE
  pm_runtime.h: explicitly requires notifier.h
  linux/dmaengine.h: fix implicit use of bitmap.h and asm/page.h
  miscdevice.h: fix up implicit use of lists and types
  stop_machine.h: fix implicit use of smp.h for smp_processor_id
  of: fix implicit use of errno.h in include/linux/of.h
  of_platform.h: delete needless include &lt;linux/module.h&gt;
  acpi: remove module.h include from platform/aclinux.h
  miscdevice.h: delete unnecessary inclusion of module.h
  device_cgroup.h: delete needless include &lt;linux/module.h&gt;
  net: sch_generic remove redundant use of &lt;linux/module.h&gt;
  net: inet_timewait_sock doesnt need &lt;linux/module.h&gt;
  ...

Fix up trivial conflicts (other header files, and  removal of the ab3550 mfd driver) in
 - drivers/media/dvb/frontends/dibx000_common.c
 - drivers/media/video/{mt9m111.c,ov6650.c}
 - drivers/mfd/ab3550-core.c
 - include/linux/dmaengine.h
</pre>
</div>
</content>
</entry>
<entry>
<title>Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc</title>
<updated>2011-11-07T01:12:03+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2011-11-07T01:12:03+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=1197ab2942f920f261952de0c392ac749a35796b'/>
<id>1197ab2942f920f261952de0c392ac749a35796b</id>
<content type='text'>
* 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc: (106 commits)
  powerpc/p3060qds: Add support for P3060QDS board
  powerpc/83xx: Add shutdown request support to MCU handling on MPC8349 MITX
  powerpc/85xx: Make kexec to interate over online cpus
  powerpc/fsl_booke: Fix comment in head_fsl_booke.S
  powerpc/85xx: issue 15 EOI after core reset for FSL CoreNet devices
  powerpc/8xxx: Fix interrupt handling in MPC8xxx GPIO driver
  powerpc/85xx: Add 'fsl,pq3-gpio' compatiable for GPIO driver
  powerpc/86xx: Correct Gianfar support for GE boards
  powerpc/cpm: Clear muram before it is in use.
  drivers/virt: add ioctl for 32-bit compat on 64-bit to fsl-hv-manager
  powerpc/fsl_msi: add support for "msi-address-64" property
  powerpc/85xx: Setup secondary cores PIR with hard SMP id
  powerpc/fsl-booke: Fix settlbcam for 64-bit
  powerpc/85xx: Adding DCSR node to dtsi device trees
  powerpc/85xx: clean up FPGA device tree nodes for Freecsale QorIQ boards
  powerpc/85xx: fix PHYS_64BIT selection for P1022DS
  powerpc/fsl-booke: Fix setup_initial_memory_limit to not blindly map
  powerpc: respect mem= setting for early memory limit setup
  powerpc: Update corenet64_smp_defconfig
  powerpc: Update mpc85xx/corenet 32-bit defconfigs
  ...

Fix up trivial conflicts in:
 - arch/powerpc/configs/40x/hcu4_defconfig
	removed stale file, edited elsewhere
 - arch/powerpc/include/asm/udbg.h, arch/powerpc/kernel/udbg.c:
	added opal and gelic drivers vs added ePAPR driver
 - drivers/tty/serial/8250.c
	moved UPIO_TSI to powerpc vs removed UPIO_DWAPB support
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
* 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc: (106 commits)
  powerpc/p3060qds: Add support for P3060QDS board
  powerpc/83xx: Add shutdown request support to MCU handling on MPC8349 MITX
  powerpc/85xx: Make kexec to interate over online cpus
  powerpc/fsl_booke: Fix comment in head_fsl_booke.S
  powerpc/85xx: issue 15 EOI after core reset for FSL CoreNet devices
  powerpc/8xxx: Fix interrupt handling in MPC8xxx GPIO driver
  powerpc/85xx: Add 'fsl,pq3-gpio' compatiable for GPIO driver
  powerpc/86xx: Correct Gianfar support for GE boards
  powerpc/cpm: Clear muram before it is in use.
  drivers/virt: add ioctl for 32-bit compat on 64-bit to fsl-hv-manager
  powerpc/fsl_msi: add support for "msi-address-64" property
  powerpc/85xx: Setup secondary cores PIR with hard SMP id
  powerpc/fsl-booke: Fix settlbcam for 64-bit
  powerpc/85xx: Adding DCSR node to dtsi device trees
  powerpc/85xx: clean up FPGA device tree nodes for Freecsale QorIQ boards
  powerpc/85xx: fix PHYS_64BIT selection for P1022DS
  powerpc/fsl-booke: Fix setup_initial_memory_limit to not blindly map
  powerpc: respect mem= setting for early memory limit setup
  powerpc: Update corenet64_smp_defconfig
  powerpc: Update mpc85xx/corenet 32-bit defconfigs
  ...

Fix up trivial conflicts in:
 - arch/powerpc/configs/40x/hcu4_defconfig
	removed stale file, edited elsewhere
 - arch/powerpc/include/asm/udbg.h, arch/powerpc/kernel/udbg.c:
	added opal and gelic drivers vs added ePAPR driver
 - drivers/tty/serial/8250.c
	moved UPIO_TSI to powerpc vs removed UPIO_DWAPB support
</pre>
</div>
</content>
</entry>
<entry>
<title>Cross Memory Attach</title>
<updated>2011-11-01T00:30:44+00:00</updated>
<author>
<name>Christopher Yeoh</name>
<email>cyeoh@au1.ibm.com</email>
</author>
<published>2011-11-01T00:06:39+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=fcf634098c00dd9cd247447368495f0b79be12d1'/>
<id>fcf634098c00dd9cd247447368495f0b79be12d1</id>
<content type='text'>
The basic idea behind cross memory attach is to allow MPI programs doing
intra-node communication to do a single copy of the message rather than a
double copy of the message via shared memory.

The following patch attempts to achieve this by allowing a destination
process, given an address and size from a source process, to copy memory
directly from the source process into its own address space via a system
call.  There is also a symmetrical ability to copy from the current
process's address space into a destination process's address space.

- Use of /proc/pid/mem has been considered, but there are issues with
  using it:
  - Does not allow for specifying iovecs for both src and dest, assuming
    preadv or pwritev was implemented either the area read from or
  written to would need to be contiguous.
  - Currently mem_read allows only processes who are currently
  ptrace'ing the target and are still able to ptrace the target to read
  from the target. This check could possibly be moved to the open call,
  but its not clear exactly what race this restriction is stopping
  (reason  appears to have been lost)
  - Having to send the fd of /proc/self/mem via SCM_RIGHTS on unix
  domain socket is a bit ugly from a userspace point of view,
  especially when you may have hundreds if not (eventually) thousands
  of processes  that all need to do this with each other
  - Doesn't allow for some future use of the interface we would like to
  consider adding in the future (see below)
  - Interestingly reading from /proc/pid/mem currently actually
  involves two copies! (But this could be fixed pretty easily)

As mentioned previously use of vmsplice instead was considered, but has
problems.  Since you need the reader and writer working co-operatively if
the pipe is not drained then you block.  Which requires some wrapping to
do non blocking on the send side or polling on the receive.  In all to all
communication it requires ordering otherwise you can deadlock.  And in the
example of many MPI tasks writing to one MPI task vmsplice serialises the
copying.

There are some cases of MPI collectives where even a single copy interface
does not get us the performance gain we could.  For example in an
MPI_Reduce rather than copy the data from the source we would like to
instead use it directly in a mathops (say the reduce is doing a sum) as
this would save us doing a copy.  We don't need to keep a copy of the data
from the source.  I haven't implemented this, but I think this interface
could in the future do all this through the use of the flags - eg could
specify the math operation and type and the kernel rather than just
copying the data would apply the specified operation between the source
and destination and store it in the destination.

Although we don't have a "second user" of the interface (though I've had
some nibbles from people who may be interested in using it for intra
process messaging which is not MPI).  This interface is something which
hardware vendors are already doing for their custom drivers to implement
fast local communication.  And so in addition to this being useful for
OpenMPI it would mean the driver maintainers don't have to fix things up
when the mm changes.

There was some discussion about how much faster a true zero copy would
go. Here's a link back to the email with some testing I did on that:

http://marc.info/?l=linux-mm&amp;m=130105930902915&amp;w=2

There is a basic man page for the proposed interface here:

http://ozlabs.org/~cyeoh/cma/process_vm_readv.txt

This has been implemented for x86 and powerpc, other architecture should
mainly (I think) just need to add syscall numbers for the process_vm_readv
and process_vm_writev. There are 32 bit compatibility versions for
64-bit kernels.

For arch maintainers there are some simple tests to be able to quickly
verify that the syscalls are working correctly here:

http://ozlabs.org/~cyeoh/cma/cma-test-20110718.tgz

Signed-off-by: Chris Yeoh &lt;yeohc@au1.ibm.com&gt;
Cc: Ingo Molnar &lt;mingo@elte.hu&gt;
Cc: "H. Peter Anvin" &lt;hpa@zytor.com&gt;
Cc: Thomas Gleixner &lt;tglx@linutronix.de&gt;
Cc: Arnd Bergmann &lt;arnd@arndb.de&gt;
Cc: Paul Mackerras &lt;paulus@samba.org&gt;
Cc: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Cc: David Howells &lt;dhowells@redhat.com&gt;
Cc: James Morris &lt;jmorris@namei.org&gt;
Cc: &lt;linux-man@vger.kernel.org&gt;
Cc: &lt;linux-arch@vger.kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
The basic idea behind cross memory attach is to allow MPI programs doing
intra-node communication to do a single copy of the message rather than a
double copy of the message via shared memory.

The following patch attempts to achieve this by allowing a destination
process, given an address and size from a source process, to copy memory
directly from the source process into its own address space via a system
call.  There is also a symmetrical ability to copy from the current
process's address space into a destination process's address space.

- Use of /proc/pid/mem has been considered, but there are issues with
  using it:
  - Does not allow for specifying iovecs for both src and dest, assuming
    preadv or pwritev was implemented either the area read from or
  written to would need to be contiguous.
  - Currently mem_read allows only processes who are currently
  ptrace'ing the target and are still able to ptrace the target to read
  from the target. This check could possibly be moved to the open call,
  but its not clear exactly what race this restriction is stopping
  (reason  appears to have been lost)
  - Having to send the fd of /proc/self/mem via SCM_RIGHTS on unix
  domain socket is a bit ugly from a userspace point of view,
  especially when you may have hundreds if not (eventually) thousands
  of processes  that all need to do this with each other
  - Doesn't allow for some future use of the interface we would like to
  consider adding in the future (see below)
  - Interestingly reading from /proc/pid/mem currently actually
  involves two copies! (But this could be fixed pretty easily)

As mentioned previously use of vmsplice instead was considered, but has
problems.  Since you need the reader and writer working co-operatively if
the pipe is not drained then you block.  Which requires some wrapping to
do non blocking on the send side or polling on the receive.  In all to all
communication it requires ordering otherwise you can deadlock.  And in the
example of many MPI tasks writing to one MPI task vmsplice serialises the
copying.

There are some cases of MPI collectives where even a single copy interface
does not get us the performance gain we could.  For example in an
MPI_Reduce rather than copy the data from the source we would like to
instead use it directly in a mathops (say the reduce is doing a sum) as
this would save us doing a copy.  We don't need to keep a copy of the data
from the source.  I haven't implemented this, but I think this interface
could in the future do all this through the use of the flags - eg could
specify the math operation and type and the kernel rather than just
copying the data would apply the specified operation between the source
and destination and store it in the destination.

Although we don't have a "second user" of the interface (though I've had
some nibbles from people who may be interested in using it for intra
process messaging which is not MPI).  This interface is something which
hardware vendors are already doing for their custom drivers to implement
fast local communication.  And so in addition to this being useful for
OpenMPI it would mean the driver maintainers don't have to fix things up
when the mm changes.

There was some discussion about how much faster a true zero copy would
go. Here's a link back to the email with some testing I did on that:

http://marc.info/?l=linux-mm&amp;m=130105930902915&amp;w=2

There is a basic man page for the proposed interface here:

http://ozlabs.org/~cyeoh/cma/process_vm_readv.txt

This has been implemented for x86 and powerpc, other architecture should
mainly (I think) just need to add syscall numbers for the process_vm_readv
and process_vm_writev. There are 32 bit compatibility versions for
64-bit kernels.

For arch maintainers there are some simple tests to be able to quickly
verify that the syscalls are working correctly here:

http://ozlabs.org/~cyeoh/cma/cma-test-20110718.tgz

Signed-off-by: Chris Yeoh &lt;yeohc@au1.ibm.com&gt;
Cc: Ingo Molnar &lt;mingo@elte.hu&gt;
Cc: "H. Peter Anvin" &lt;hpa@zytor.com&gt;
Cc: Thomas Gleixner &lt;tglx@linutronix.de&gt;
Cc: Arnd Bergmann &lt;arnd@arndb.de&gt;
Cc: Paul Mackerras &lt;paulus@samba.org&gt;
Cc: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Cc: David Howells &lt;dhowells@redhat.com&gt;
Cc: James Morris &lt;jmorris@namei.org&gt;
Cc: &lt;linux-man@vger.kernel.org&gt;
Cc: &lt;linux-arch@vger.kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
</feed>
