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Message-ID: <20151113221212.GJ569@nuc-i3427.alporthouse.com> Date: Fri, 13 Nov 2015 22:12:12 +0000 From: Chris Wilson <chris@...is-wilson.co.uk> To: Jens Axboe <axboe@...nel.dk> Cc: Mike Galbraith <umgwanakikbuti@...il.com>, Daniel Vetter <daniel.vetter@...ll.ch>, DRI Development <dri-devel@...ts.freedesktop.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: __i915_spin_request() sucks On Fri, Nov 13, 2015 at 09:22:52AM -0700, Jens Axboe wrote: > On 11/13/2015 09:13 AM, Mike Galbraith wrote: > >On Fri, 2015-11-13 at 08:36 -0700, Jens Axboe wrote: > >>Previous patch was obvious pre-coffee crap, this should work for using > >>ktime to spin max 1usec. > > > >1us seems a tad low. I doubt the little wooden gears and pulleys of my > >core2 Toshiba Satellite lappy can get one loop ground out in a usec :) > > Maybe it is, it's based off the original intent of the function, > though. See the original commit referenced. I've been looking at numbers from one laptop and I can set the timeout at 2us before we see a steep decline in what is more or less synchronous request handling (which affects a variety of rendering workloads). Looking around, other busy loops seem to use local_clock() (i.e. rdstcll with a fair wind). Is that worth using here? -Chris -- Chris Wilson, Intel Open Source Technology Centre -- 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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