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| author | Wanpeng Li <wanpengli@tencent.com> | 2018-10-09 09:02:08 +0800 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2018-10-17 00:25:54 +0200 |
| commit | 3b8a5df6c4dc6df2ab17d099fb157032f80bdca2 (patch) | |
| tree | 1215438b19491bfc167ed694bd0b8805fdff8317 /arch/x86/kvm/x86.c | |
| parent | efebf0aaec3de4df2bdb2949ebaacacd82de37db (diff) | |
| download | linux-3b8a5df6c4dc6df2ab17d099fb157032f80bdca2.tar.bz2 | |
KVM: LAPIC: Tune lapic_timer_advance_ns automatically
In cloud environment, lapic_timer_advance_ns is needed to be tuned for every CPU
generations, and every host kernel versions(the kvm-unit-tests/tscdeadline_latency.flat
is 5700 cycles for upstream kernel and 9600 cycles for our 3.10 product kernel,
both preemption_timer=N, Skylake server).
This patch adds the capability to automatically tune lapic_timer_advance_ns
step by step, the initial value is 1000ns as 'commit d0659d946be0 ("KVM: x86:
add option to advance tscdeadline hrtimer expiration")' recommended, it will be
reduced when it is too early, and increased when it is too late. The guest_tsc
and tsc_deadline are hard to equal, so we assume we are done when the delta
is within a small scope e.g. 100 cycles. This patch reduces latency
(kvm-unit-tests/tscdeadline_latency, busy waits, preemption_timer enabled)
from ~2600 cyles to ~1200 cyles on our Skylake server.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ca717737347e..1f3f95557703 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -136,7 +136,7 @@ static u32 __read_mostly tsc_tolerance_ppm = 250; module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR); /* lapic timer advance (tscdeadline mode only) in nanoseconds */ -unsigned int __read_mostly lapic_timer_advance_ns = 0; +unsigned int __read_mostly lapic_timer_advance_ns = 1000; module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); EXPORT_SYMBOL_GPL(lapic_timer_advance_ns); |