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tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed

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Checking for and processing RCU-nocb deferred wakeup upon user/guest
entry is only relevant when nohz_full runs on the local CPU, otherwise
the periodic tick should take care of it.

Make sure we don't needlessly pollute these fast-paths as a -3%
performance regression on a will-it-scale.per_process_ops has been
reported so far.

Fixes: 47b8ff194c (entry: Explicitly flush pending rcuog wakeup before last rescheduling point)
Fixes: 4ae7dc97f7 (entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point)
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210527113441.465489-1-frederic@kernel.org
This commit is contained in:
Frederic Weisbecker
2021-05-27 13:34:41 +02:00
committed by Peter Zijlstra
parent 02da26ad5e
commit f268c3737e
4 changed files with 13 additions and 3 deletions
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3
include/linux/entry-kvm.h
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@@ -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();
}
/**