Date: Wed, 28 Jun 2017 17:58:51 +0200
From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>, DanielWagnerwagi@monom.org,
        Boqun Feng <boqun.feng@gmail.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Ming Lei <ming.lei@redhat.com>, "Li, Yi" <yi1.li@linux.intel.com>,
        "AKASHI, Takahiro" <takahiro.akashi@linaro.org>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Petr Mladek <pmladek@suse.com>, Andrew Lutomirski <luto@kernel.org>,
        Kees Cook <keescook@chromium.org>, David Howells <dhowells@redhat.com>,
        Alan Cox <alan@linux.intel.com>, "Theodore Ts'o" <tytso@mit.edu>,
        oss-drivers@netronome.com
Subject: Re: [PATCH] firmware: wake all waiters
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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