From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: __i915_spin_request() sucks Date: Thu, 12 Nov 2015 13:36:32 -0700 Message-ID: <5644F850.2060803@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-kernel-owner@vger.kernel.org To: Daniel Vetter , chris@chris-wilson.co.uk Cc: DRI Development , LKML List-Id: dri-devel@lists.freedesktop.org Hi, So a few months ago I got an XPS13 laptop, the one with the high res screen. GUI performance was never really that great, I attributed it to coming from a more powerful laptop, and the i915 driving a lot of pixels. But yesterday I browsed from my wife's macbook, and was blown away. Wow, scrolling in chrome SUCKS on the xps13. Not just scrolling, basically anything in chrome. Molasses. So I got sick of it, fired up a quick perf record, did a bunch of stuff in chrome. No super smoking guns, but one thing did stick out - the path leading to __i915_spin_request(). So today, I figured I'd try just killing that spin. If it fails, we'll punt to normal completions, so easy change. And wow, MASSIVE difference. I can now scroll in chrome and not rage! It's like the laptop is 10x faster now. Ran git blame, and found: commit 2def4ad99befa25775dd2f714fdd4d92faec6e34 Author: Chris Wilson Date: Tue Apr 7 16:20:41 2015 +0100 drm/i915: Optimistically spin for the request completion and read the commit message. Doesn't sound that impressive. Especially not for something that screws up interactive performance by a LOT. What's the deal? Revert? -- Jens Axboe