From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ankur Arora <ankur.a.arora@oracle.com>,
linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org,
luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com,
hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de,
jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com,
boris.ostrovsky@oracle.com, konrad.wilk@oracle.com,
jgross@suse.com, andrew.cooper3@citrix.com,
Joel Fernandes <joel@joelfernandes.org>,
Youssef Esmat <youssefesmat@chromium.org>,
Vineeth Pillai <vineethrp@google.com>,
Suleiman Souhlal <suleiman@google.com>,
Ingo Molnar <mingo@kernel.org>,
Daniel Bristot de Oliveira <bristot@kernel.org>
Subject: Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice
Date: Thu, 26 Oct 2023 14:59:13 -0400 [thread overview]
Message-ID: <7871472b-a0c4-4475-9671-69a3244f956d@efficios.com> (raw)
In-Reply-To: <CAHk-=whnyt2TccpDaWGTbDsVkKApL3c2FtDPMEwuTmeu_cEL8Q@mail.gmail.com>
On 2023-10-26 14:50, Linus Torvalds wrote:
> On Thu, 26 Oct 2023 at 08:36, Mathieu Desnoyers
> <mathieu.desnoyers@efficios.com> wrote:
>>
>>> asm volatile("xchg %b0,%1"
>>
>> which has an implicit lock prefix (xchg with a memory operand is a
>> special-case):
>
> Yeah, this is why we do "percpu_xchg()" - which does not want locked
> semantics - as a "cmpxchg" loop.
>
> Steven, check out
>
> arch/x86/include/asm/percpu.h
>
> 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.
Thanks,
Mathieu
>
> Linus
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
next prev parent reply other threads:[~2023-10-26 18:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-26 3:54 [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice Steven Rostedt
2023-10-26 10:59 ` Peter Zijlstra
2023-10-26 11:14 ` Steven Rostedt
2023-10-26 18:36 ` Mathieu Desnoyers
2023-10-26 18:50 ` Linus Torvalds
2023-10-26 18:59 ` Mathieu Desnoyers [this message]
2023-10-26 19:36 ` Steven Rostedt
2023-10-26 20:45 ` Steven Rostedt
[not found] ` <644da047-2f7a-4d55-a339-f2dc28d2c852@efficios.com>
[not found] ` <20231027122442.5c76dd62@gandalf.local.home>
2023-10-27 16:35 ` Mathieu Desnoyers
2023-10-27 16:49 ` Steven Rostedt
2023-10-30 12:56 ` Mathieu Desnoyers
2023-10-30 13:45 ` Steven Rostedt
2023-10-30 18:05 ` Mathieu Desnoyers
2023-10-30 18:19 ` Steven Rostedt
2023-10-30 18:27 ` Mathieu Desnoyers
2023-10-30 18:39 ` Steven Rostedt
2023-10-26 19:20 ` Steven Rostedt
2023-10-26 21:35 ` Steven Rostedt
2023-10-27 21:52 ` Steven Rostedt
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