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Open Source and information security mailing list archives
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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/
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