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

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Date:   Wed, 28 Jun 2017 12:03:11 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     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

Hi Luis!

On Wed, 28 Jun 2017, Luis R. Rodriguez wrote:

>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?

I have nothing against removing it.

Thanks,
Davidlohr