From: Frederic Weisbecker <frederic@kernel.org>
To: Usama Arif <usama.arif@linux.dev>
Cc: tglx@kernel.org, anna-maria@linutronix.de,
linux-kernel@vger.kernel.org, mingo@kernel.org,
hannes@cmpxchg.org, shakeel.butt@linux.dev, riel@surriel.com,
kernel-team@meta.com
Subject: Re: [PATCH] tick/nohz: Remove redundant IRQ save/restore
Date: Wed, 16 Sep 2026 16:49:45 +0200 [thread overview]
Message-ID: <aqqsiSDCpvkfxFTI@localhost.localdomain> (raw)
In-Reply-To: <20260916141530.3423310-1-usama.arif@linux.dev>
Le Wed, Sep 16, 2026 at 07:15:30AM -0700, Usama Arif a écrit :
> 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>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
--
Frederic Weisbecker
SUSE Labs
prev parent reply other threads:[~2026-09-16 14:49 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-16 14:15 Usama Arif
2026-09-16 14:49 ` Frederic Weisbecker [this message]
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