linux-kernel - Re: [PATCH v2 2/2 sched_ext/for-6.12] sched_ext: Use sched_clock_cpu() instead of rq_clock_task() in touch_core

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Message-ID: <20240830180143.GF5055@maniforge>
Date: Fri, 30 Aug 2024 13:01:43 -0500
From: David Vernet <void@...ifault.com>
To: Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
	kernel-team@...a.com
Subject: Re: [PATCH v2 2/2 sched_ext/for-6.12] sched_ext: Use
 sched_clock_cpu() instead of rq_clock_task() in touch_core_sched()

On Fri, Aug 30, 2024 at 07:54:41AM -1000, Tejun Heo wrote:
> Since 3cf78c5d01d6 ("sched_ext: Unpin and repin rq lock from
> balance_scx()"), sched_ext's balance path terminates rq_pin in the outermost
> function. This is simpler and in line with what other balance functions are
> doing but it loses control over rq->clock_update_flags which makes
> assert_clock_udpated() trigger if other CPUs pins the rq lock.
> 
> The only place this matters is touch_core_sched() which uses the timestamp
> to order tasks from sibling rq's. Switch to sched_clock_cpu(). Later, it may
> be better to use per-core dispatch sequence number.
> 
> v2: Use sched_clock_cpu() instead of ktime_get_ns() per David.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Fixes: 3cf78c5d01d6 ("sched_ext: Unpin and repin rq lock from balance_scx()")
> Cc: David Vernet <void@...ifault.com>
> Cc: Peter Zijlstra <peterz@...radead.org>

Acked-by: David Vernet <void@...ifault.com>

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