linux-kernel - Re: [PATCH] firmware: wake all waiters

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Message-ID: <20170628155851.GF21846@wotan.suse.de>
Date:   Wed, 28 Jun 2017 17:58:51 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        DanielWagnerwagi@...om.org, Boqun Feng <boqun.feng@...il.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Ming Lei <ming.lei@...hat.com>,
        "Li, Yi" <yi1.li@...ux.intel.com>,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        David Howells <dhowells@...hat.com>,
        Alan Cox <alan@...ux.intel.com>, Theodore Ts'o <tytso@....edu>,
        oss-drivers@...ronome.com
Subject: Re: [PATCH] firmware: wake all waiters

On Wed, Jun 28, 2017 at 06:45:14AM -0700, Davidlohr Bueso wrote:
> On Tue, 27 Jun 2017, Luis R. Rodriguez wrote:
> 
> > diff --git a/include/linux/swait.h b/include/linux/swait.h
> > index 4a4e180d0a35..14fcf23cece4 100644
> > --- a/include/linux/swait.h
> > +++ b/include/linux/swait.h
> > @@ -29,7 +29,10 @@
> >  *
> >  * As a side effect of this; the data structures are slimmer.
> >  *
> > - * One would recommend using this wait queue where possible.
> 
> So I think this was added due to the smaller footprint and fewer
> cycles that swait has compared to the traditional (bulkier)
> waitqueues. While probably not worth it, I guess we could offer
> super-simple waitqueues (sswait? :-) which do not have the rt caveats
> and uses a regular spinlock. The wakeup_all() call would not drop
> the lock upon every wakeup as we are stripping the waitqueue not
> for determinism, but for overhead. To mitigate this, we might
> also want to use wake_q for reduced hold q->lock hold times.
> 
> But I don't think its worth yet another wait interface.
> Alternatively, it crossed my mind we could also have wakeup_all()
> use in the regular waitqueues, but I'd have to audit all the
> current users to make sure we could actually do this.

But this open-welcoming invite for swait then, should it go?

  Luis