From: Peter Zijlstra <[email protected]>
To: Sebastian Andrzej Siewior <[email protected]>
Cc: [email protected], [email protected],
Ingo Molnar <[email protected]>,
Juri Lelli <[email protected]>,
Vincent Guittot <[email protected]>,
Dietmar Eggemann <[email protected]>,
Steven Rostedt <[email protected]>,
Ben Segall <[email protected]>, Mel Gorman <[email protected]>,
Jens Axboe <[email protected]>,
Thomas Gleixner <[email protected]>
Subject: Re: [PATCH 2/2] sched: Cache task_struct::flags in sched_submit_work()
Date: Wed, 19 Aug 2020 22:11:27 +0200 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On Wed, Aug 19, 2020 at 10:00:25PM +0200, Sebastian Andrzej Siewior wrote:
> sched_submit_work() is considered to be a hot path. The preempt_disable()
> instruction is a compiler barrier and forces the compiler to load
> task_struct::flags for the second comparison.
> By using a local variable, the compiler can load the value once and keep it in
> a register for the second comparison.
>
> Verified on x86-64 with gcc-10.
>
> Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
> ---
>
> Optimisation at molecule level, part two. Drop this in case this branch
> isn't consider *that* hot and the cache hot value can be loaded again.
> But then the value is around and be speculated early on :)
That's fine, task->flags can only be changed by current.
Patches look good to me, I'll stuff them in tomorrow. Thanks!
next prev parent reply other threads:[~2020-08-19 20:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-19 12:37 [RFC PATCH] sched: Invoke io_wq_worker_sleeping() with enabled preemption Sebastian Andrzej Siewior
2020-08-19 13:15 ` peterz
2020-08-19 13:18 ` Jens Axboe
2020-08-19 19:44 ` [PATCH] io_wq: Make io_wqe::lock a raw_spinlock_t Sebastian Andrzej Siewior
2020-09-01 8:41 ` [PATCH v2] " Sebastian Andrzej Siewior
2020-09-01 14:17 ` Jens Axboe
2020-08-19 13:33 ` [RFC PATCH] sched: Invoke io_wq_worker_sleeping() with enabled preemption Sebastian Andrzej Siewior
2020-08-19 14:21 ` peterz
2020-08-19 19:55 ` [PATCH 1/2] sched: Bring the PF_IO_WORKER and PF_WQ_WORKER bits closer together Sebastian Andrzej Siewior
2020-08-19 20:00 ` [PATCH 2/2] sched: Cache task_struct::flags in sched_submit_work() Sebastian Andrzej Siewior
2020-08-19 20:11 ` Peter Zijlstra [this message]
2020-09-07 12:58 ` [PATCH 1/2] sched: Bring the PF_IO_WORKER and PF_WQ_WORKER bits closer together Will Deacon
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