Currently the notifier of pvclock_gtod_notify() get invoked
frequently due to the periodic update_wall_time(). This might
slow down the system a little bit as there might be redundant
execution code path and unnecessary lock contention
in update_pvclock_gtod(), which was found when I was doing
suspend/resume speed testings. As pvclock_gtod_notify()
should be invoked only when clocksource has changed, according to
Commit 16e8d74d2da9 ("KVM: x86: notifier for clocksource changes")
, either we can add a new notifier for clocksource switch,
or we can simply bypass the following code in pvclock_gtod_notify()
earlier if there is no clocksource switch.Cc: Paolo Bonzini <[email protected]> Cc: "Radim Krcmar" <[email protected]> Cc: Marcelo Tosatti <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Wanpeng Li <[email protected]> Signed-off-by: Chen Yu <[email protected]> --- arch/x86/kvm/x86.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 445c51b..54aa32d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5961,13 +5961,14 @@ static int pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused, struct pvclock_gtod_data *gtod = &pvclock_gtod_data; struct timekeeper *tk = priv; + if (likely(gtod->clock.vclock_mode == VCLOCK_TSC)) + return 0; update_pvclock_gtod(tk); /* disable master clock if host does not trust, or does not * use, TSC clocksource */ - if (gtod->clock.vclock_mode != VCLOCK_TSC && - atomic_read(&kvm_guest_has_master_clock) != 0) + if (atomic_read(&kvm_guest_has_master_clock) != 0) queue_work(system_long_wq, &pvclock_gtod_work); return 0; -- 2.7.4
