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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
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