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Date: Fri, 15 Apr 2011 12:33:12 -0400 From: Mike Frysinger <vapier@...too.org> To: Pavel Machek <pavel@....cz> 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 ? On Fri, Apr 15, 2011 at 12:29, Pavel Machek wrote: >> > > I believe the code is correct as is. >> > >> > that isnt what the code / documentation says. unless i'm reading them >> > wrong, both seem to indicate that the proposed patch is what we >> > actually want. >> >> 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. -mike -- 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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