From: Pavel Machek <pavel@ucw.cz>
To: Mike Frysinger <vapier@gentoo.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
uclinux-dist-devel@blackfin.uclinux.org,
linux-pm@lists.linux-foundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [uclinux-dist-devel] [linux-pm] freezer: should barriers be smp ?
Date: Fri, 15 Apr 2011 18:57:37 +0200 [thread overview]
Message-ID: <20110415165737.GA23812@elf.ucw.cz> (raw)
In-Reply-To: <BANLkTikaymG-5-YoTnG2SPJCnBtXPpfHBQ@mail.gmail.com>
> >> The existing code is correct but it isn't optimal.
> >>
> >> wmb() and rmb() are heavy-duty operations, and you don't want to call
> >> them when they aren't needed. That's exactly what smp_wmb() and
> >> smp_rmb() are for -- they call wmb() and rmb(), but only in SMP
> >> kernels.
> >>
> >> Unless you need to synchronize with another processor (not necessarily
> >> a CPU, it could be something embedded within a device), you should
> >> always use smp_wmb() and smp_rmb() rather than wmb() and rmb().
> >
> > Maybe; but this code is not performance critical and I believe being
> > obvious here is better...
>
> isnt it though ? especially when we talk about suspending/resuming on
> embedded systems to get more savings over just cpu idle ? we want
> that latency to be as low as possible.
Feel free to measure the difference. I bet it is lost in noise,
freezer just is not _that_ hot path.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
next prev parent reply other threads:[~2011-04-15 16:57 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-13 6:14 Mike Frysinger
2011-04-13 20:58 ` Rafael J. Wysocki
2011-04-13 21:02 ` Mike Frysinger
2011-04-13 21:05 ` Pavel Machek
2011-04-13 21:11 ` [uclinux-dist-devel] " Mike Frysinger
2011-04-13 21:53 ` Rafael J. Wysocki
2011-04-13 22:11 ` [linux-pm] " Alan Stern
2011-04-13 22:34 ` [linux-pm] [uclinux-dist-devel] freezer: should barriers be smp? Rafael J. Wysocki
2011-04-14 14:55 ` Alan Stern
2011-04-14 22:34 ` Rafael J. Wysocki
2011-04-15 14:32 ` Alan Stern
2011-04-13 22:22 ` [uclinux-dist-devel] freezer: should barriers be smp ? Mike Frysinger
2011-04-13 22:49 ` Rafael J. Wysocki
2011-04-13 22:53 ` Rafael J. Wysocki
2011-04-13 22:57 ` Mike Frysinger
2011-04-13 23:12 ` Rafael J. Wysocki
2011-04-14 15:13 ` [linux-pm] " Alan Stern
2011-04-14 22:40 ` Rafael J. Wysocki
2011-04-13 22:04 ` [linux-pm] [uclinux-dist-devel] " Alan Stern
2011-04-15 16:29 ` Pavel Machek
2011-04-15 16:33 ` [uclinux-dist-devel] [linux-pm] " Mike Frysinger
2011-04-15 16:57 ` Pavel Machek [this message]
2011-04-15 23:11 ` Rafael J. Wysocki
2011-04-15 23:24 ` Mike Frysinger
2011-04-15 23:30 ` Rafael J. Wysocki
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