Re: [uclinux-dist-devel] [linux-pm] freezer: should barriers be smp ?
From: Mike Frysinger
Date: Fri Apr 15 2011 - 12:33:39 EST
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. Âunless 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. ÂThat's exactly what smp_wmb() and
>> smp_rmb() are for -- they call wmb() and rmb(), but only in SMP
>> 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.
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