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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id m9sm2547869qkn.59.2021.12.03.11.00.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Dec 2021 11:00:25 -0800 (PST) Date: Fri, 3 Dec 2021 14:00:24 -0500 From: Josef Bacik To: Valentin Schneider Cc: peterz@infradead.org, vincent.guittot@linaro.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org Subject: Re: [REGRESSION] 5-10% increase in IO latencies with nohz balance patch Message-ID: References: <87ee6yc00j.mognet@arm.com> <87bl22byq2.mognet@arm.com> <878rx6bia5.mognet@arm.com> <87wnklaoa8.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87wnklaoa8.mognet@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Dec 03, 2021 at 12:03:27PM +0000, Valentin Schneider wrote: > On 30/11/21 00:26, Valentin Schneider wrote: > > On 29/11/21 14:49, Josef Bacik wrote: > >> On Mon, Nov 29, 2021 at 06:31:17PM +0000, Valentin Schneider wrote: > >>> On 29/11/21 13:15, Josef Bacik wrote: > >>> > On Mon, Nov 29, 2021 at 06:03:24PM +0000, Valentin Schneider wrote: > >>> >> Would you happen to have execution traces by any chance? If not I should be > >>> >> able to get one out of that fsperf thingie. > >>> >> > >>> > > >>> > I don't, if you want to tell me how I can do it right now. I've disabled > >>> > everything on this box for now so it's literally just sitting there waiting to > >>> > have things done to it. Thanks, > >>> > > >>> > >>> I see you have Ftrace enabled in your config, so that ought to do it: > >>> > >>> trace-cmd record -e 'sched:*' -e 'cpu_idle' $your_test_cmd > >>> > >> > >> http://toxicpanda.com/performance/trace.dat > >> > >> it's like 16mib. Enjoy, > >> > > > > Neat, thanks! > > > > Runqueue depth seems to be very rarely greater than 1, tasks with ~1ms > > runtime and lots of sleeping (also bursty kworker activity with activations > > of tens of µs), and some cores (Internet tells me that Xeon Bronze 3204 > > doesn't have SMT) spend most of their time idling. Not the most apocalyptic > > task placement vs ILB selection, but the task activation patterns roughly > > look like what I was thinking of - there might be hope for me yet. > > > > I'll continue the headscratching after tomorrow's round of thinking juice. > > > > Could you give the 4 top patches, i.e. those above > 8c92606ab810 ("sched/cpuacct: Make user/system times in cpuacct.stat more precise") > a try? > > https://git.gitlab.arm.com/linux-arm/linux-vs.git -b mainline/sched/nohz-next-update-regression > > I gave that a quick test on the platform that caused me to write the patch > you bisected and looks like it didn't break the original fix. If the above > counter-measures aren't sufficient, I'll have to go poke at your > reproducers... > It's better but still around 6% regression. If I compare these patches to the average of the last few days worth of runs you're 5% better than before, so progress but not completely erased. metric baseline current stdev diff ====================================================================== write_io_kbytes 125000 125000 0 0.00% read_clat_ns_p99 0 0 0 0.00% write_bw_bytes 1.73e+08 1.74e+08 5370366.50 0.69% read_iops 0 0 0 0.00% write_clat_ns_p50 18265.60 18150.40 345.21 -0.63% read_io_kbytes 0 0 0 0.00% read_io_bytes 0 0 0 0.00% write_clat_ns_p99 84684.80 90316.80 6607.94 6.65% read_bw_bytes 0 0 0 0.00% elapsed 1 1 0 0.00% write_lat_ns_min 0 0 0 0.00% sys_cpu 91.22 91.00 1.40 -0.24% write_lat_ns_max 0 0 0 0.00% read_lat_ns_min 0 0 0 0.00% write_iops 42308.54 42601.71 1311.12 0.69% read_lat_ns_max 0 0 0 0.00% read_clat_ns_p50 0 0 0 0.00% Thanks, Josef