linux-kernel - Re: [PATCH V1] fuse: give wakeup hints to the scheduler

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Message-ID: <Ya9m0ME1pom49b+D@hirez.programming.kicks-ass.net>
Date:   Tue, 7 Dec 2021 14:51:12 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Ingo Molnar <mingo@...hat.com>, quic_stummala@...cinc.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        quic_pkondeti@...cinc.com, quic_sayalil@...cinc.com,
        quic_aiquny@...cinc.com, quic_zljing@...cinc.com,
        quic_blong@...cinc.com, quic_richardp@...cinc.com,
        quic_cdevired@...cinc.com,
        Pradeep P V K <quic_pragalla@...cinc.com>
Subject: Re: [PATCH V1] fuse: give wakeup hints to the scheduler

On Tue, Dec 07, 2021 at 02:45:49PM +0100, Peter Zijlstra wrote:

> > What would be much nicer, is to look at all the threads on the waitq
> > and pick one that previously ran on the current CPU if there's one.
> > Could this be implemented?
> 
> It would violate the FIFO semantics of _exclusive.

That said, look at
kernel/locking/percpu-rwsem.c:percpu_rwsem_wake_function() for how to do
really terrible things with waitqueues, possibly including what you
suggest.