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Message-ID: <644da047-2f7a-4d55-a339-f2dc28d2c852@efficios.com>
Date: Fri, 27 Oct 2023 12:09:56 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ankur Arora <ankur.a.arora@...cle.com>, linux-mm@...ck.org,
x86@...nel.org, akpm@...ux-foundation.org, luto@...nel.org,
bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
mingo@...hat.com, juri.lelli@...hat.com,
vincent.guittot@...aro.org, willy@...radead.org, mgorman@...e.de,
jon.grimm@....com, bharata@....com, raghavendra.kt@....com,
boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
jgross@...e.com, andrew.cooper3@...rix.com,
Joel Fernandes <joel@...lfernandes.org>,
Youssef Esmat <youssefesmat@...omium.org>,
Vineeth Pillai <vineethrp@...gle.com>,
Suleiman Souhlal <suleiman@...gle.com>,
Ingo Molnar <mingo@...nel.org>,
Daniel Bristot de Oliveira <bristot@...nel.org>
Subject: Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice
On 2023-10-26 16:45, Steven Rostedt wrote:
> On Thu, 26 Oct 2023 14:59:13 -0400
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
>
>>> for a rough implementation of a 'xchg()' without SMP coherency, just
>>> cpu-local one (ie atomic wrt being preempted by the kernel, but not
>>> atomic wrt other CPU's accessing the same variable concurrently)
>>
>> Actually Steven does not need a xchg to test-and-set a single bit which
>> is only accessed concurrently between kernel and userspace from the same
>> thread. Either "bts" or "andb" should work fine.
>
> Hmm, how would bts work? Doesn't that just set a bit?
Yes, and it saves the bit state in the CF flag before setting it.
If you need to clear a bit then it would be "btr".
>
> I need to clear one bit while seeing if another bit is set. I could also
> use subl, as that would also atomically clear the bit.
Ah ok, I did not get that you needed to test for a different bit than
the one you clear.
Thanks,
Mathieu
>
> -- Steve
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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