diff options
| author | Marcelo Tosatti <mtosatti@redhat.com> | 2013-07-10 22:21:57 -0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2013-07-18 12:29:30 +0200 |
| commit | e04c5d76b0cfb66cadd900cf147526f2271884b8 (patch) | |
| tree | a303b66c1fc1ae7786148d2f50e8b0b86290162b /arch/x86/vdso/vclock_gettime.c | |
| parent | b3897a49e22fc173efa77527a447c714f753f681 (diff) | |
remove sched notifier for cross-cpu migrations
Linux as a guest on KVM hypervisor, the only user of the pvclock
vsyscall interface, does not require notification on task migration
because:
1. cpu ID number maps 1:1 to per-CPU pvclock time info.
2. per-CPU pvclock time info is updated if the
underlying CPU changes.
3. that version is increased whenever underlying CPU
changes.
Which is sufficient to guarantee nanoseconds counter
is calculated properly.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Diffstat (limited to 'arch/x86/vdso/vclock_gettime.c')
| -rw-r--r-- | arch/x86/vdso/vclock_gettime.c | 16 |
1 files changed, 8 insertions, 8 deletions
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c index c74436e687bf..72074d528400 100644 --- a/arch/x86/vdso/vclock_gettime.c +++ b/arch/x86/vdso/vclock_gettime.c @@ -85,15 +85,18 @@ static notrace cycle_t vread_pvclock(int *mode) cycle_t ret; u64 last; u32 version; - u32 migrate_count; u8 flags; unsigned cpu, cpu1; /* - * When looping to get a consistent (time-info, tsc) pair, we - * also need to deal with the possibility we can switch vcpus, - * so make sure we always re-fetch time-info for the current vcpu. + * Note: hypervisor must guarantee that: + * 1. cpu ID number maps 1:1 to per-CPU pvclock time info. + * 2. that per-CPU pvclock time info is updated if the + * underlying CPU changes. + * 3. that version is increased whenever underlying CPU + * changes. + * */ do { cpu = __getcpu() & VGETCPU_CPU_MASK; @@ -104,8 +107,6 @@ static notrace cycle_t vread_pvclock(int *mode) pvti = get_pvti(cpu); - migrate_count = pvti->migrate_count; - version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags); /* @@ -117,8 +118,7 @@ static notrace cycle_t vread_pvclock(int *mode) cpu1 = __getcpu() & VGETCPU_CPU_MASK; } while (unlikely(cpu != cpu1 || (pvti->pvti.version & 1) || - pvti->pvti.version != version || - pvti->migrate_count != migrate_count)); + pvti->pvti.version != version)); if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT))) *mode = VCLOCK_NONE; |