KVM_PV_REASON_PAGE_NOT_PRESENT kicks cpu out of idleness, but we haven't
marked that spot as an exit from idleness.
Not doing so can cause RCU warnings such as:
[ 732.788386] ===============================
[ 732.789803] [ INFO: suspicious RCU usage. ]
[ 732.790032] 3.7.0-rc1-next-20121019-sasha-00002-g6d8d02d-dirty #63 Tainted: G W
[ 732.790032] -------------------------------
[ 732.790032] include/linux/rcupdate.h:738 rcu_read_lock() used illegally while idle!
[ 732.790032]
[ 732.790032] other info that might help us debug this:
[ 732.790032]
[ 732.790032]
[ 732.790032] RCU used illegally from idle CPU!
[ 732.790032] rcu_scheduler_active = 1, debug_locks = 1
[ 732.790032] RCU used illegally from extended quiescent state!
[ 732.790032] 2 locks held by trinity-child31/8252:
[ 732.790032] #0: (&rq->lock){-.-.-.}, at: [<ffffffff83a67528>] __schedule+0x178/0x8f0
[ 732.790032] #1: (rcu_read_lock){.+.+..}, at: [<ffffffff81152bde>] cpuacct_charge+0xe/0x200
[ 732.790032]
[ 732.790032] stack backtrace:
[ 732.790032] Pid: 8252, comm: trinity-child31 Tainted: G W 3.7.0-rc1-next-20121019-sasha-00002-g6d8d02d-dirty #63
[ 732.790032] Call Trace:
[ 732.790032] [<ffffffff8118266b>] lockdep_rcu_suspicious+0x10b/0x120
[ 732.790032] [<ffffffff81152c60>] cpuacct_charge+0x90/0x200
[ 732.790032] [<ffffffff81152bde>] ? cpuacct_charge+0xe/0x200
[ 732.790032] [<ffffffff81158093>] update_curr+0x1a3/0x270
[ 732.790032] [<ffffffff81158a6a>] dequeue_entity+0x2a/0x210
[ 732.790032] [<ffffffff81158ea5>] dequeue_task_fair+0x45/0x130
[ 732.790032] [<ffffffff8114ae29>] dequeue_task+0x89/0xa0
[ 732.790032] [<ffffffff8114bb9e>] deactivate_task+0x1e/0x20
[ 732.790032] [<ffffffff83a67c29>] __schedule+0x879/0x8f0
[ 732.790032] [<ffffffff8117e20d>] ? trace_hardirqs_off+0xd/0x10
[ 732.790032] [<ffffffff810a37a5>] ? kvm_async_pf_task_wait+0x1d5/0x2b0
[ 732.790032] [<ffffffff83a67cf5>] schedule+0x55/0x60
[ 732.790032] [<ffffffff810a37c4>] kvm_async_pf_task_wait+0x1f4/0x2b0
[ 732.790032] [<ffffffff81139e50>] ? abort_exclusive_wait+0xb0/0xb0
[ 732.790032] [<ffffffff81139c25>] ? prepare_to_wait+0x25/0x90
[ 732.790032] [<ffffffff810a3a66>] do_async_page_fault+0x56/0xa0
[ 732.790032] [<ffffffff83a6a6e8>] async_page_fault+0x28/0x30
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
The distinction between CONFIG_KVM_CLOCK and CONFIG_KVM_GUEST is not so clear anymore, as demonstrated by recent bugs caused by poor handling of on/off combinations of these options. Merge CONFIG_KVM_CLOCK into CONFIG_KVM_GUEST. Reported-By: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
else, host continues to update stealtime after reboot, which can corrupt e.g. initramfs area. found when tracking down initramfs unpack error on initial reboot (with qemu-kvm -smp 2, no problem with single-core). Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Use apic_set_eoi_write, apic_write to avoid meedling in core apic driver data structures directly. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
While debugging I noticed that unlike all the other hypervisor code in the kernel, kvm does not have an entry for x86_hyper which is used in detect_hypervisor_platform() which results in a nice printk in the syslog. This is only really a stub function but it does make kvm more consistent with the other hypervisors. Signed-off-by: Prarit Bhargava <prarit@redhat.com> Cc: Avi Kivity <avi@redhat.com> Cc: Gleb Natapov <gleb@redhat.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Marcelo Tostatti <mtosatti@redhat.com> Cc: kvm@vger.kernel.org Signed-off-by: Avi Kivity <avi@redhat.com>
The idea is simple: there's a bit, per APIC, in guest memory,
that tells the guest that it does not need EOI.
Guest tests it using a single est and clear operation - this is
necessary so that host can detect interrupt nesting - and if set, it can
skip the EOI MSR.
I run a simple microbenchmark to show exit reduction
(note: for testing, need to apply follow-up patch
'kvm: host side for eoi optimization' + a qemu patch
I posted separately, on host):
Before:
Performance counter stats for 'sleep 1s':
47,357 kvm:kvm_entry [99.98%]
0 kvm:kvm_hypercall [99.98%]
0 kvm:kvm_hv_hypercall [99.98%]
5,001 kvm:kvm_pio [99.98%]
0 kvm:kvm_cpuid [99.98%]
22,124 kvm:kvm_apic [99.98%]
49,849 kvm:kvm_exit [99.98%]
21,115 kvm:kvm_inj_virq [99.98%]
0 kvm:kvm_inj_exception [99.98%]
0 kvm:kvm_page_fault [99.98%]
22,937 kvm:kvm_msr [99.98%]
0 kvm:kvm_cr [99.98%]
0 kvm:kvm_pic_set_irq [99.98%]
0 kvm:kvm_apic_ipi [99.98%]
22,207 kvm:kvm_apic_accept_irq [99.98%]
22,421 kvm:kvm_eoi [99.98%]
0 kvm:kvm_pv_eoi [99.99%]
0 kvm:kvm_nested_vmrun [99.99%]
0 kvm:kvm_nested_intercepts [99.99%]
0 kvm:kvm_nested_vmexit [99.99%]
0 kvm:kvm_nested_vmexit_inject [99.99%]
0 kvm:kvm_nested_intr_vmexit [99.99%]
0 kvm:kvm_invlpga [99.99%]
0 kvm:kvm_skinit [99.99%]
57 kvm:kvm_emulate_insn [99.99%]
0 kvm:vcpu_match_mmio [99.99%]
0 kvm:kvm_userspace_exit [99.99%]
2 kvm:kvm_set_irq [99.99%]
2 kvm:kvm_ioapic_set_irq [99.99%]
23,609 kvm:kvm_msi_set_irq [99.99%]
1 kvm:kvm_ack_irq [99.99%]
131 kvm:kvm_mmio [99.99%]
226 kvm:kvm_fpu [100.00%]
0 kvm:kvm_age_page [100.00%]
0 kvm:kvm_try_async_get_page [100.00%]
0 kvm:kvm_async_pf_doublefault [100.00%]
0 kvm:kvm_async_pf_not_present [100.00%]
0 kvm:kvm_async_pf_ready [100.00%]
0 kvm:kvm_async_pf_completed
1.002100578 seconds time elapsed
After:
Performance counter stats for 'sleep 1s':
28,354 kvm:kvm_entry [99.98%]
0 kvm:kvm_hypercall [99.98%]
0 kvm:kvm_hv_hypercall [99.98%]
1,347 kvm:kvm_pio [99.98%]
0 kvm:kvm_cpuid [99.98%]
1,931 kvm:kvm_apic [99.98%]
29,595 kvm:kvm_exit [99.98%]
24,884 kvm:kvm_inj_virq [99.98%]
0 kvm:kvm_inj_exception [99.98%]
0 kvm:kvm_page_fault [99.98%]
1,986 kvm:kvm_msr [99.98%]
0 kvm:kvm_cr [99.98%]
0 kvm:kvm_pic_set_irq [99.98%]
0 kvm:kvm_apic_ipi [99.99%]
25,953 kvm:kvm_apic_accept_irq [99.99%]
26,132 kvm:kvm_eoi [99.99%]
26,593 kvm:kvm_pv_eoi [99.99%]
0 kvm:kvm_nested_vmrun [99.99%]
0 kvm:kvm_nested_intercepts [99.99%]
0 kvm:kvm_nested_vmexit [99.99%]
0 kvm:kvm_nested_vmexit_inject [99.99%]
0 kvm:kvm_nested_intr_vmexit [99.99%]
0 kvm:kvm_invlpga [99.99%]
0 kvm:kvm_skinit [99.99%]
284 kvm:kvm_emulate_insn [99.99%]
68 kvm:vcpu_match_mmio [99.99%]
68 kvm:kvm_userspace_exit [99.99%]
2 kvm:kvm_set_irq [99.99%]
2 kvm:kvm_ioapic_set_irq [99.99%]
28,288 kvm:kvm_msi_set_irq [99.99%]
1 kvm:kvm_ack_irq [99.99%]
131 kvm:kvm_mmio [100.00%]
588 kvm:kvm_fpu [100.00%]
0 kvm:kvm_age_page [100.00%]
0 kvm:kvm_try_async_get_page [100.00%]
0 kvm:kvm_async_pf_doublefault [100.00%]
0 kvm:kvm_async_pf_not_present [100.00%]
0 kvm:kvm_async_pf_ready [100.00%]
0 kvm:kvm_async_pf_completed
1.002039622 seconds time elapsed
We see that # of exits is almost halved.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
It turned to be totally unneeded. The reason the code was introduced is so that KVM can prefault swapped in page, but prefault can fail even if mm is pinned since page table can change anyway. KVM handles this situation correctly though and does not inject spurious page faults. Fixes: "INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected" warning while running LTP inside a KVM guest using the recent -next kernel. Reported-by: Sasha Levin <levinsasha928@gmail.com> Signed-off-by: Gleb Natapov <gleb@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
"Page ready" async PF can kick vcpu out of idle state much like IRQ. We need to tell RCU about this. Reported-by: Sasha Levin <levinsasha928@gmail.com> Signed-off-by: Gleb Natapov <gleb@redhat.com> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Avi Kivity <avi@redhat.com>
So here's a boot tested patch on top of Jason's series that does
all the cleanups I talked about and turns jump labels into a
more intuitive to use facility. It should also address the
various misconceptions and confusions that surround jump labels.
Typical usage scenarios:
#include <linux/static_key.h>
struct static_key key = STATIC_KEY_INIT_TRUE;
if (static_key_false(&key))
do unlikely code
else
do likely code
Or:
if (static_key_true(&key))
do likely code
else
do unlikely code
The static key is modified via:
static_key_slow_inc(&key);
...
static_key_slow_dec(&key);
The 'slow' prefix makes it abundantly clear that this is an
expensive operation.
I've updated all in-kernel code to use this everywhere. Note
that I (intentionally) have not pushed through the rename
blindly through to the lowest levels: the actual jump-label
patching arch facility should be named like that, so we want to
decouple jump labels from the static-key facility a bit.
On non-jump-label enabled architectures static keys default to
likely()/unlikely() branches.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Jason Baron <jbaron@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: a.p.zijlstra@chello.nl
Cc: mathieu.desnoyers@efficios.com
Cc: davem@davemloft.net
Cc: ddaney.cavm@gmail.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20120222085809.GA26397@elte.hu
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This has not been used for some years now. It's time to remove it. Signed-off-by: Chris Wright <chrisw@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>