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tick/nohz: Remove redundant local_irq_save()/restore()

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tick_nohz_update_jiffies() is only reached through tick_irq_enter() from
hard interrupt entry, where local interrupts are already disabled.

tick_do_update_jiffies64() requires interrupts to be disabled. The
local_irq_save()/local_irq_restore() pair around it therefore provides no
additional interrupt exclusion.

Remove it and assert the caller invariant instead.

On x86-64, this avoids the redundant RFLAGS save, CLI, saved-IF test and
conditional branch on the tick-stopped path.

On a 252-CPU host running a Thrift RPC service, tick_irq_enter() ran
165,116 times/s out of 212-244k interrupts/s. Only calls with
TS_FLAG_STOPPED reach the optimized path, so this is an upper bound on
its execution rate.

Signed-off-by: Usama Arif <usama.arif@linux.dev>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://patch.msgid.link/20260916141530.3423310-1-usama.arif@linux.dev
This commit is contained in:
Usama Arif 2026-09-16 07:15:30 -07:00 committed by Thomas Gleixner
parent a59a940ff8
commit 75990fb534
1 changed files with 2 additions and 5 deletions
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7
kernel/time/tick-sched.c
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@ -738,14 +738,11 @@ bool tick_nohz_tick_stopped_cpu(int cpu)
*/
static void tick_nohz_update_jiffies(ktime_t now)
{
unsigned long flags;
/* Reached only from irq_enter_rcu(), i.e. hard interrupt entry. */
lockdep_assert_irqs_disabled();
__this_cpu_write(tick_cpu_sched.idle_waketime, now);
local_irq_save(flags);
tick_do_update_jiffies64(now);
local_irq_restore(flags);
touch_softlockup_watchdog_sched();
}