On 02/10/2015 02:59 PM, Andy Lutomirski wrote: > On 02/10/2015 06:41 AM, riel@xxxxxxxxxx wrote: >> From: Rik van Riel <riel@xxxxxxxxxx> >> >> The host kernel is not doing anything while the CPU is executing >> a KVM guest VCPU, so it can be marked as being in an extended >> quiescent state, identical to that used when running user space >> code. >> >> The only exception to that rule is when the host handles an >> interrupt, which is already handled by the irq code, which >> calls rcu_irq_enter and rcu_irq_exit. >> >> The guest_enter and guest_exit functions already switch vtime >> accounting independent of context tracking. Leave those calls >> where they are, instead of moving them into the context tracking >> code. >> >> Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> >> --- >> include/linux/context_tracking.h | 6 ++++++ >> include/linux/context_tracking_state.h | 1 + >> include/linux/kvm_host.h | 3 ++- >> 3 files changed, 9 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/context_tracking.h >> b/include/linux/context_tracking.h >> index 954253283709..b65fd1420e53 100644 >> --- a/include/linux/context_tracking.h >> +++ b/include/linux/context_tracking.h >> @@ -80,10 +80,16 @@ static inline void guest_enter(void) >> vtime_guest_enter(current); >> else >> current->flags |= PF_VCPU; >> + >> + if (context_tracking_is_enabled()) >> + context_tracking_enter(IN_GUEST); > > Why the if statement? > > Also, have you checked how much this hurts guest lightweight entry/exit > latency? Context tracking is shockingly expensive for reasons I don't > fully understand, but hopefully most of it is the vtime stuff. Guest_enter and guest_exit already do the vtime stuff today. This patch series adds the rcu stuff, and modifies context_tracking_enter & context_tracking_exit to not do the vtime stuff twice. > (Context tracking is *so* expensive that I almost think we should set the > performance taint flag if we enable it, assuming that flag ended up > getting merged. Also, we should make context tracking faster.) I am all for making it faster :) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
