Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 10 Nov 2014 11:39:56 -0800 | Subject | Re: [LKP] [x86_64,entry] f04e05b81e4: -62.7% time.user_time |
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On Thu, Nov 6, 2014 at 10:40 PM, Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote: > On Thu, Nov 06, 2014 at 10:26:23PM -0800, Andy Lutomirski wrote: >> On Thu, Nov 6, 2014 at 10:00 PM, LKP <lkp@01.org> wrote: >> > FYI, we noticed the below changes on >> > >> > git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git x86/entry >> > commit f04e05b81e4d9ae88bee379f12176f551a24394a ("x86_64,entry: Use sysret to return to userspace when possible") >> > >> > >> > f2ee9bebb99dd4a4 f04e05b81e4d9ae88bee379f12 testbox/testcase/testparams >> > ---------------- -------------------------- >> > %stddev %change %stddev >> > \ | \ >> > 24.09 ą 4% -62.7% 8.99 ą 3% lkp-wsx02/aim9/performance-300s-creat-clo >> > 24.09 -62.7% 8.99 GEO-MEAN time.user_time >> > >> >> I don't really know how to interpret this. Is this a good thing or a bad thing? > > TBH, I don't, either. Here we just list the changes we captured, which > is then for your information to decide it's good or bad. > >> >> I actually expect this change to be a dramatic speedup for some >> workloads. > > Would you like to share your workload? If so, I can add them to our > testing system, and give feedback to you when datat is available.
My workload is just syscall performance under different conditions. There's no obvious interesting benchmark, although I may write one at some point.
> >> Any chance you can send me the .config, kernel command >> line, and whether you have any tracing features enabled? > > .config and dmesg are attached.
Hmm. I'm not entirely sure what's going on. I think that you have NO_HZ_FULL active, but I can't see what's actually activating it. My initial attempt to replicate this failed, but I see a big performance gain if CONFIG_CONTEXT_TRACKING_FORCE=y, so I suspect that you've just managed to activate context tracking without forcing it.
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