Re: [PATCH v3] drm/i915: Optimistically spin for the request completion

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	intel-gfx@lists.freedesktop.org,
	Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: Re: [PATCH v3] drm/i915: Optimistically spin for the request completion
Date: Thu, 12 Mar 2015 17:32:26 +0000	[thread overview]
Message-ID: <5501CDAA.10506@linux.intel.com> (raw)
In-Reply-To: <20150312165012.GB29296@nuc-i3427.alporthouse.com>

On 03/12/2015 04:50 PM, Chris Wilson wrote:
> On Thu, Mar 12, 2015 at 04:41:10PM +0000, Tvrtko Ursulin wrote:
>> Yes I didn't mean that - but to have a boolean spinning-wait=on/off.
>> Maybe default to "on" on HZ=1000 with preemption, or the opposite,
>> something like that.
>
> I don't see the point in having the complication, until someone
> complains. In my defense, I will point to the optimistic mutex spinning
> equally having no configurable option. And since the idea is that you
> only hit this if you are abusing i915 (e.g. benchmarking, or you have a
> readback on the critical patch, or if we haven't implemented
> semaphores), I would rather fix those scenarios as they arrive rather
> than giving the user an option to break.

I simply pointed out a theoretical potential to burn more CPU on 
servers. If you know that is unlikely or only theoretical that's fine by me.

But I'll say I was more convinced before you mentioned "until someone 
complains" and "option to break". :)

Regards,

Tvrtko
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