On 11/12/2015 01:36 PM, Jens Axboe wrote: > 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 <chris at chris-wilson.co.uk> > 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?
BTW, this: "Limit the spinning to a single jiffie (~1us) at most" is totally wrong. I have HZ=100 on my laptop. That's 10ms. 10ms! Even if I had HZ=1000, that'd still be 1ms of spinning. That's seriously screwed up, guys. -- Jens Axboe
