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authorFrederic Weisbecker <frederic@kernel.org>2021-05-27 13:34:41 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-05-31 10:14:49 +0200
commitf268c3737ecaefcfeecfb4cb5e44958a8976f067 (patch)
tree895c3ffc8d716b3d00851b569eb183f73a95d9fc /kernel/entry
parent02da26ad5ed6ea8680e5d01f20661439611ed776 (diff)
downloadlinux-f268c3737ecaefcfeecfb4cb5e44958a8976f067.tar.bz2
tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed
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: 47b8ff194c1f (entry: Explicitly flush pending rcuog wakeup before last rescheduling point) Fixes: 4ae7dc97f726 (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
Diffstat (limited to 'kernel/entry')
-rw-r--r--kernel/entry/common.c5
1 files changed, 3 insertions, 2 deletions
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);