From: Alexandre Bique <bique.alexandre@gmail.com>
To: Konstantin Kharlamov <hi-angel@yandex.ru>
Cc: Florian Weimer <fweimer@redhat.com>,
Alexandre Bique via Libc-help <libc-help@sourceware.org>
Subject: Re: Yield to specific thread?
Date: Thu, 20 May 2021 13:54:02 +0200 [thread overview]
Message-ID: <CAP737oLvhkHeyKzHG948Bp2xgWx-c9NHqd=mfdc+DfCw0ZJJQA@mail.gmail.com> (raw)
In-Reply-To: <75365b7da217aab24c686e18399bc017aa6c9ac7.camel@yandex.ru>
Oh I think I fixed it using 3 mutexes.
Alexandre Bique
On Thu, May 20, 2021 at 1:20 PM Konstantin Kharlamov <hi-angel@yandex.ru> wrote:
>
> On Thu, 2021-05-20 at 13:09 +0200, Alexandre Bique via Libc-help wrote:
> > On Thu, May 20, 2021 at 1:03 PM Florian Weimer <fweimer@redhat.com> wrote:
> > >
> > > * Alexandre Bique via Libc-help:
> > >
> > > > Ideally I'd like to do:
> > > > A produces a request
> > > > A sched_yield_to(B)
> > > > B processes the request
> > > > B sched_yield_to(A)
> > >
> > > This looks like an application for a condition variable or perhaps a
> > > barrier. If there is just a single writer, the kernel should wake up
> > > the desired thread.
> >
> > I don't think conditions or barriers would solve the problem. Because
> > they would just put the waiting threads on the wake up queue like the
> > read() on the pipe would.
>
> I assume it should work. I remember Torvalds ranting about people using sched_yield() for the wrong reasons¹, and he mentioned mutex (which apparently worked for you) as one of possible solutions. Quoting:
>
> > Good locking simply needs to be more directed than what "sched_yield()" can ever give you outside of a UP system without caches. It needs to actively tell the system what you're yielding to (and optimally it would also tell the system about whether you care about fairness/latency or not - a lot of loads don't).
> >
> > But that's not "sched_yield()" - that's something different. It's generally something like std::mutex, pthread_mutex_lock(), or perhaps a tuned thing that uses an OS-specific facility like "futex", where you do the nonblocking (and non-contended) case in user space using a shared memory location, but when you get contention you tell the OS what you're waiting for (and what you're waking up).
>
>
> 1: https://www.realworldtech.com/forum/?threadid=189711&curpostid=189752
>
next prev parent reply other threads:[~2021-05-20 11:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-20 10:42 Alexandre Bique
2021-05-20 11:02 ` Florian Weimer
2021-05-20 11:09 ` Alexandre Bique
2021-05-20 11:20 ` Konstantin Kharlamov
2021-05-20 11:54 ` Alexandre Bique [this message]
2021-05-25 18:21 ` Adhemerval Zanella
2021-05-26 9:36 ` Tadeus Prastowo
2021-05-26 14:09 ` Alexandre Bique
2021-05-20 12:27 ` Godmar Back
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