linux.git/arch/s390/kernel/vtime.c, branch v6.9 Linux kernel source tree s390/vtime: fix average steal time calculation 2024-03-13T08:23:44+00:00 Mete Durlu meted@linux.ibm.com 2024-03-06T11:31:52+00:00 367c50f78451d3bd7ad70bc5c89f9ba6dec46ca9 Current average steal timer calculation produces volatile and inflated values. The only user of this value is KVM so far and it uses that to decide whether or not to yield the vCPU which is seeing steal time. KVM compares average steal timer to a threshold and if the threshold is past then it does not allow CPU polling and yields it to host, else it keeps the CPU by polling. Since KVM's steal time threshold is very low by default (%10) it most likely is not effected much by the bloated average steal timer values because the operating region is pretty small. However there might be new users in the future who might rely on this number. Fix average steal timer calculation by changing the formula from: avg_steal_timer = avg_steal_timer / 2 + steal_timer; to the following: avg_steal_timer = (avg_steal_timer + steal_timer) / 2; This ensures that avg_steal_timer is actually a naive average of steal timer values. It now closely follows steal timer values but of course in a smoother manner. Fixes: 152e9b8676c6 ("s390/vtime: steal time exponential moving average") Signed-off-by: Mete Durlu <meted@linux.ibm.com> Acked-by: Heiko Carstens <hca@linux.ibm.com> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> 
Current average steal timer calculation produces volatile and inflated
values. The only user of this value is KVM so far and it uses that to
decide whether or not to yield the vCPU which is seeing steal time.
KVM compares average steal timer to a threshold and if the threshold
is past then it does not allow CPU polling and yields it to host, else
it keeps the CPU by polling.
Since KVM's steal time threshold is very low by default (%10) it most
likely is not effected much by the bloated average steal timer values
because the operating region is pretty small. However there might be
new users in the future who might rely on this number. Fix average
steal timer calculation by changing the formula from:

	avg_steal_timer = avg_steal_timer / 2 + steal_timer;

to the following:

	avg_steal_timer = (avg_steal_timer + steal_timer) / 2;

This ensures that avg_steal_timer is actually a naive average of steal
timer values. It now closely follows steal timer values but of course
in a smoother manner.

Fixes: 152e9b8676c6 ("s390/vtime: steal time exponential moving average")
Signed-off-by: Mete Durlu <meted@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
cputime: remove cputime_to_nsecs fallback 2022-12-27T11:52:17+00:00 Nicholas Piggin npiggin@gmail.com 2022-12-20T07:07:05+00:00 c89970202a1153b2fc230e89f90c180bd5bcbcef The archs that use cputime_to_nsecs() internally provide their own definition and don't need the fallback. cputime_to_usecs() unused except in this fallback, and is not defined anywhere. This removes the final remnant of the cputime_t code from the kernel. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Alexander Gordeev <agordeev@linux.ibm.com> Link: https://lore.kernel.org/r/20221220070705.2958959-1-npiggin@gmail.com 
The archs that use cputime_to_nsecs() internally provide their own
definition and don't need the fallback. cputime_to_usecs() unused except
in this fallback, and is not defined anywhere.

This removes the final remnant of the cputime_t code from the kernel.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Link: https://lore.kernel.org/r/20221220070705.2958959-1-npiggin@gmail.com
s390: assume stckf is always present 2022-03-10T14:58:17+00:00 Vasily Gorbik gor@linux.ibm.com 2022-02-25T09:38:23+00:00 10bc15ba3a853723267016274b58be6c9a6e64da With z10 as minimum supported machine generation the store-clock-fast facility (25) is always present and checked in als code. Drop alternatives and always use stckf. Acked-by: Ilya Leoshkevich <iii@linux.ibm.com> Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> 
With z10 as minimum supported machine generation the store-clock-fast
facility (25) is always present and checked in als code.
Drop alternatives and always use stckf.

Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
s390/vtime: fix increased steal time accounting 2021-03-15T18:09:25+00:00 Gerald Schaefer gerald.schaefer@linux.ibm.com 2021-03-10T13:23:37+00:00 d54cb7d54877d529bc1e0e1f47a3dd082f73add3 Commit 152e9b8676c6e ("s390/vtime: steal time exponential moving average") inadvertently changed the input value for account_steal_time() from "cputime_to_nsecs(steal)" to just "steal", resulting in broken increased steal time accounting. Fix this by changing it back to "cputime_to_nsecs(steal)". Fixes: 152e9b8676c6e ("s390/vtime: steal time exponential moving average") Cc: <stable@vger.kernel.org> # 5.1 Reported-by: Sabine Forkel <sabine.forkel@de.ibm.com> Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> 
Commit 152e9b8676c6e ("s390/vtime: steal time exponential moving average")
inadvertently changed the input value for account_steal_time() from
"cputime_to_nsecs(steal)" to just "steal", resulting in broken increased
steal time accounting.

Fix this by changing it back to "cputime_to_nsecs(steal)".

Fixes: 152e9b8676c6e ("s390/vtime: steal time exponential moving average")
Cc: <stable@vger.kernel.org> # 5.1
Reported-by: Sabine Forkel <sabine.forkel@de.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
s390/vtime: use cpu alternative for stck/stckf 2021-02-09T14:57:06+00:00 Heiko Carstens hca@linux.ibm.com 2021-02-02T15:59:50+00:00 1c7673476b82983768c6a4dd78775f817f0e0f88 Use a cpu alternative to switch between stck and stckf instead of making it compile time dependent. This will also make kernels compiled for old machines, but running on newer machines, use stckf. Signed-off-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> 
Use a cpu alternative to switch between stck and stckf instead of
making it compile time dependent. This will also make kernels compiled
for old machines, but running on newer machines, use stckf.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
s390/vtime: fix inline assembly clobber list 2021-02-09T14:57:05+00:00 Heiko Carstens hca@linux.ibm.com 2021-02-02T15:45:37+00:00 b29c5093820d333eef22f58cd04ec0d089059c39 The stck/stckf instruction used within the inline assembly within do_account_vtime() changes the condition code. This is not reflected with the clobber list, and therefore might result in incorrect code generation. It seems unlikely that the compiler could generate incorrect code considering the surrounding C code, but it must still be fixed. Cc: <stable@vger.kernel.org> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> 
The stck/stckf instruction used within the inline assembly within
do_account_vtime() changes the condition code. This is not reflected
with the clobber list, and therefore might result in incorrect code
generation.

It seems unlikely that the compiler could generate incorrect code
considering the surrounding C code, but it must still be fixed.

Cc: <stable@vger.kernel.org>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
sched/vtime: Consolidate IRQ time accounting 2020-12-02T19:20:05+00:00 Frederic Weisbecker frederic@kernel.org 2020-12-02T11:57:30+00:00 8a6a5920d3286eb0eae9f36a4ec4fc9df511eccb The 3 architectures implementing CONFIG_VIRT_CPU_ACCOUNTING_NATIVE all have their own version of irq time accounting that dispatch the cputime to the appropriate index: hardirq, softirq, system, idle, guest... from an all-in-one function. Instead of having these ad-hoc versions, move the cputime destination dispatch decision to the core code and leave only the actual per-index cputime accounting to the architecture. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20201202115732.27827-4-frederic@kernel.org 
The 3 architectures implementing CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
all have their own version of irq time accounting that dispatch the
cputime to the appropriate index: hardirq, softirq, system, idle,
guest... from an all-in-one function.

Instead of having these ad-hoc versions, move the cputime destination
dispatch decision to the core code and leave only the actual per-index
cputime accounting to the architecture.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201202115732.27827-4-frederic@kernel.org
s390/vtime: Use the generic IRQ entry accounting 2020-12-02T19:20:04+00:00 Frederic Weisbecker frederic@kernel.org 2020-12-02T11:57:29+00:00 2b91ec9f551b56751cde48792f1c0a1130358844 s390 has its own version of IRQ entry accounting because it doesn't account the idle time the same way the other architectures do. Only the actual idle sleep time is accounted as idle time, the rest of the idle task execution is accounted as system time. Make the generic IRQ entry accounting aware of architectures that have their own way of accounting idle time and convert s390 to use it. This prepares s390 to get involved in further consolidations of IRQ time accounting. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20201202115732.27827-3-frederic@kernel.org 
s390 has its own version of IRQ entry accounting because it doesn't
account the idle time the same way the other architectures do. Only
the actual idle sleep time is accounted as idle time, the rest of the
idle task execution is accounted as system time.

Make the generic IRQ entry accounting aware of architectures that have
their own way of accounting idle time and convert s390 to use it.

This prepares s390 to get involved in further consolidations of IRQ
time accounting.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201202115732.27827-3-frederic@kernel.org
sched/cputime: Remove symbol exports from IRQ time accounting 2020-12-02T19:20:04+00:00 Frederic Weisbecker frederic@kernel.org 2020-12-02T11:57:28+00:00 7197688b2006357da75a014e0a76be89ca9c2d46 account_irq_enter_time() and account_irq_exit_time() are not called from modules. EXPORT_SYMBOL_GPL() can be safely removed from the IRQ cputime accounting functions called from there. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20201202115732.27827-2-frederic@kernel.org 
account_irq_enter_time() and account_irq_exit_time() are not called
from modules. EXPORT_SYMBOL_GPL() can be safely removed from the IRQ
cputime accounting functions called from there.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201202115732.27827-2-frederic@kernel.org
sched/cputime: Rename vtime_account_system() to vtime_account_kernel() 2019-10-09T10:39:25+00:00 Frederic Weisbecker frederic@kernel.org 2019-10-03T16:17:44+00:00 f83eeb1a01689b2691f6f56629ac9f66de8d41c2 vtime_account_system() decides if we need to account the time to the system (__vtime_account_system()) or to the guest (vtime_account_guest()). So this function is a misnomer as we are on a higher level than "system". All we know when we call that function is that we are accounting kernel cputime. Whether it belongs to guest or system time is a lower level detail. Rename this function to vtime_account_kernel(). This will clarify things and avoid too many underscored vtime_account_system() versions. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Wanpeng Li <wanpengli@tencent.com> Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com> Link: https://lkml.kernel.org/r/20191003161745.28464-2-frederic@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> 
vtime_account_system() decides if we need to account the time to the
system (__vtime_account_system()) or to the guest (vtime_account_guest()).

So this function is a misnomer as we are on a higher level than
"system". All we know when we call that function is that we are
accounting kernel cputime. Whether it belongs to guest or system time
is a lower level detail.

Rename this function to vtime_account_kernel(). This will clarify things
and avoid too many underscored vtime_account_system() versions.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191003161745.28464-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>