Messages in this thread | | | Date | Wed, 19 May 2021 13:27:00 +0800 | From | Oliver Sang <> | Subject | Re: [entry] 47b8ff194c: will-it-scale.per_process_ops -3.0% regression |
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hi, Peter Zijlstra,
On Fri, May 14, 2021 at 12:13:22PM +0200, Peter Zijlstra wrote: > On Fri, May 14, 2021 at 01:11:27AM +0200, Frederic Weisbecker wrote: > > > That sounds good, but two things: > > > > 1) Even if context tracking is not running, we still need to handle > > deferred wakeups on idle. But all user/guest/idle currently use the > > same function. > > > > 2) Context tracking may be running even when full nohz is not. But here only > > full nohz is concerned. > > > > So the change should rather be as follows (completely untested!). > > I rather put the static key check in tick.h in order not to involve > > deep dependencies inside rcupdate.h (especially rcupdate.h -> tick.h -> sched.h) > > Compiles and boots for me, 0day folks, could you please test this makes > the reported regression go away?
sorry for late.
on which base should we apply below patch? we tried to apply upon 4ae7dc97f726e ("entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point") and v5.12, but both build failed like below:
ERROR: modpost: "tick_nohz_full_mask" [arch/x86/kvm/kvm.ko] undefined!
or is there any particular kconfig need to enable? (the kconfig which we used to build 47b8ff194c is in original report which maybe you could help have a look what we may miss)
Thanks
> > > diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h > > index 8b2b1d68b954..136b8d97d8c0 100644 > > --- a/include/linux/entry-kvm.h > > +++ b/include/linux/entry-kvm.h > > @@ -3,6 +3,7 @@ > > #define __LINUX_ENTRYKVM_H > > > > #include <linux/entry-common.h> > > +#include <linux/tick.h> > > > > /* Transfer to guest mode work */ > > #ifdef CONFIG_KVM_XFER_TO_GUEST_WORK > > @@ -57,7 +58,7 @@ int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu); > > static inline void xfer_to_guest_mode_prepare(void) > > { > > lockdep_assert_irqs_disabled(); > > - rcu_nocb_flush_deferred_wakeup(); > > + tick_nohz_user_enter_prepare(); > > } > > > > /** > > diff --git a/include/linux/tick.h b/include/linux/tick.h > > index 0bb80a7f05b9..bfd571f18cfd 100644 > > --- a/include/linux/tick.h > > +++ b/include/linux/tick.h > > @@ -11,6 +11,7 @@ > > #include <linux/context_tracking_state.h> > > #include <linux/cpumask.h> > > #include <linux/sched.h> > > +#include <linux/rcupdate.h> > > > > #ifdef CONFIG_GENERIC_CLOCKEVENTS > > extern void __init tick_init(void); > > @@ -304,4 +305,10 @@ static inline void tick_nohz_task_switch(void) > > __tick_nohz_task_switch(); > > } > > > > +static inline void tick_nohz_user_enter_prepare(void) > > +{ > > + if (tick_nohz_full_cpu(smp_processor_id())) > > + rcu_nocb_flush_deferred_wakeup(); > > +} > > + > > #endif > > diff --git a/kernel/entry/common.c b/kernel/entry/common.c > > index a0b3b04fb596..bf16395b9e13 100644 > > --- a/kernel/entry/common.c > > +++ b/kernel/entry/common.c > > @@ -5,6 +5,7 @@ > > #include <linux/highmem.h> > > #include <linux/livepatch.h> > > #include <linux/audit.h> > > +#include <linux/tick.h> > > > > #include "common.h" > > > > @@ -186,7 +187,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, > > local_irq_disable_exit_to_user(); > > > > /* Check if any of the above work has queued a deferred wakeup */ > > - rcu_nocb_flush_deferred_wakeup(); > > + tick_nohz_user_enter_prepare(); > > > > ti_work = READ_ONCE(current_thread_info()->flags); > > } > > @@ -202,7 +203,7 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs) > > lockdep_assert_irqs_disabled(); > > > > /* Flush pending rcuog wakeup before the last need_resched() check */ > > - rcu_nocb_flush_deferred_wakeup(); > > + tick_nohz_user_enter_prepare(); > > > > if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) > > ti_work = exit_to_user_mode_loop(regs, ti_work);
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