Received-SPF: pass (google.com: domain of linux-kernel+bounces-130597-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
References: <969ccc0f-d909-4b45-908e-e98279777733@metaparadigm.com>
 <CAHk-=wj3khqjXnHmShPj+tZvC=SyUitTZ7BkDO-rqu_aCVPrXA@mail.gmail.com> <1a116a43-fd2e-4f03-8a17-75816fc62717@metaparadigm.com>
In-Reply-To: <1a116a43-fd2e-4f03-8a17-75816fc62717@metaparadigm.com>
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 3 Apr 2024 13:57:11 -0700
Message-ID: <CAHk-=wiOqTAX7nwQqHJ2Ti3dbxM-HrUJq3FD_Gjua5qW=QAoTg@mail.gmail.com>
Subject: Re: user-space concurrent pipe buffer scheduler interactions
To: Michael Clark <michael@metaparadigm.com>
Cc: Jens Axboe <axboe@kernel.dk>, Ingo Molnar <mingo@redhat.com>, 
	Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

On Wed, 3 Apr 2024 at 13:52, Michael Clark <michael@metaparadigm.com> wrote:
>
> On 4/4/24 05:56, Linus Torvalds wrote:
> > On Tue, 2 Apr 2024 at 13:54, Michael Clark <michael@metaparadigm.com> wrote:
> >>
> >> I am working on a low latency cross-platform concurrent pipe buffer
> >> using C11 threads and atomics.
> >
> > You will never get good performance doing spinlocks in user space
> > unless you actually tell the scheduler about the spinlocks, and have
> > some way to actually sleep on contention.
> >
> > Which I don't see you as having.
>
> We can work on this.

It's been tried.

Nobody ever found a use-case that is sufficiently convincing, but see
the write-up at

   https://lwn.net/Articles/944895/

for a pointer to at least attempts.

               Linus