linux-kernel - Re: [uclinux-dist-devel] [linux-pm] freezer: should barriers be smp ?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110415165737.GA23812@elf.ucw.cz>
Date:	Fri, 15 Apr 2011 18:57:37 +0200
From:	Pavel Machek <pavel@....cz>
To:	Mike Frysinger <vapier@...too.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [uclinux-dist-devel] [linux-pm] freezer: should barriers be
 smp ?

> >> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/