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From: Thomas Gleixner <tglx@linutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>
Cc: Christian Brauner <christian.brauner@ubuntu.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [GIT PULL] sigqueue cache fix
Date: Wed, 07 Jul 2021 11:47:47 +0200	[thread overview]
Message-ID: <878s2iqwu4.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <CAHk-=wjrd6-ZHyQGznpM+O0CtTHjzZ5P2Ozddh68WmDH9c+hBg@mail.gmail.com>

Linus,

On Mon, Jun 28 2021 at 12:02, Linus Torvalds wrote:
> And as the whole - and only - point of the sigqueue cache was a very
> subtle performance and latency issue, I don't think we want to use
> locks or atomics. It's why my revert commit suggests re-purposing the
> "percpu_cmpxchg()" functionality: that would likely be a good model at
> least for x86 and arm.
>
> But while we have "percpu_cmpxchg()", I don't think we currently don't
> really have that kind of operation where it
>
>  (a) works on a non-percpu variable (but we can force casts, I guess)
>
>  (b) has "acquire" semantics
>
> We do have the *atomic* cmpxchg with acquire semantics, but atomics
> are rather more expensive than we'd probably really want.

first of all, sorry for being non-responsive on this. I'll have a fresh
look at this with your comments in mind and be more careful.

Thanks,

        tglx

  reply	other threads:[~2021-07-07  9:47 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-24  7:13 [GIT PULL] sigqueue cache fix Ingo Molnar
2021-06-24 16:29 ` Linus Torvalds
2021-06-27 18:52   ` Linus Torvalds
2021-06-27 20:40     ` Linus Torvalds
2021-06-28  5:14       ` Ingo Molnar
2021-06-28  5:22         ` Ingo Molnar
2021-06-28  5:30           ` Ingo Molnar
2021-06-28 17:06         ` Linus Torvalds
2021-06-28 18:46           ` Ingo Molnar
2021-06-28 19:02             ` Linus Torvalds
2021-07-07  9:47               ` Thomas Gleixner [this message]
2021-06-24 16:34 ` pr-tracker-bot

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