From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: __i915_spin_request() sucks Date: Fri, 13 Nov 2015 15:16:11 -0700 Message-ID: <5646612B.20805@kernel.dk> References: <5644F850.2060803@kernel.dk> <5644F941.9090505@kernel.dk> <20151112221908.GA26194@nuc-i3427.alporthouse.com> <56451812.2050704@kernel.dk> <20151113091558.GN6247@nuc-i3427.alporthouse.com> <20151113153629.GB8939@kernel.dk> <1447431225.5655.66.camel@gmail.com> <56460E5C.6000602@kernel.dk> <20151113221212.GJ569@nuc-i3427.alporthouse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20151113221212.GJ569@nuc-i3427.alporthouse.com> Sender: linux-kernel-owner@vger.kernel.org To: Chris Wilson , Mike Galbraith , Daniel Vetter , DRI Development , LKML List-Id: dri-devel@lists.freedesktop.org On 11/13/2015 03:12 PM, Chris Wilson wrote: > 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). Alright, at least that's a vast improvement from 10ms. If you send me something tested, I can try it here. > Looking around, other busy loops seem to use local_clock() (i.e. rdstcll > with a fair wind). Is that worth using here? Honestly, don't think it matters too much for this case. You'd have to disable preempt to use local_clock(), fwiw. It is a faster variant though, but the RT people might hate you for 2us preempt disables :-) -- Jens Axboe