Messages in this thread | | | Date | Sun, 18 Apr 2010 18:59:06 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [RFC patch] CFS fix place entity spread issue (v2) |
| |
* Linus Torvalds (torvalds@linux-foundation.org) wrote: > > > On Sun, 18 Apr 2010, Mathieu Desnoyers wrote: > > > > CFS fix place entity spread issue (v2) > > > > Huge CFS vruntime spread (18 minutes) has been observed with LTTng while simply > > running Xorg on a uniprocessor machine. Detailed explanation in my ELC2010 > > presentation at: > > Hmm. I tested this patch with my favourite non-scientific desktop load > test: do web browsing while doing a kernel compile with "make -j16" (after > doing a "git clean -dqfx" and "ccache -C" to get rid of old object files > and ccache). > > This is on a dual-core (with SMT, so 4 threads) Core i5, so "make -j16" > overcommits the CPU's quite a bit. > > And quite frankly, I think your patch makes things much worse. I don't > have numbers, but it felt much choppier and slower to do scrolling in > firefox o moving windows around while the load average is 20+. > > My testload is in no way objective, nor necessarily any good, but it's the > one I happen to use, and while it's subjective, I think the difference was > pretty clear and not good. > > Linus
Degradation of this particular workload is expected, because the nature of the large CFS spread issue favors Xorg: it gets litterally minutes of available vruntime, while most other threads (e.g. kernel build, audio playing, etc..) suffer from this.
I'll try to play a bit with this (I got plenty of time to kill at the airport today, missed my connecting flight back from San Francisco). Ideally, we might want to try to find a way to ensure that place_entity() is kind to sleepers, but without putting them before min_vruntime. I don't have any SMP machine with Xorg handy, but I'll try to push my UP laptop a bit more heavily with a kernel build.
If we are lucky enough, we might just have to twist a knob or two to make Xorg more responsive.
Thanks,
Mathieu
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
| |