On Thu, May 26, 2011 at 5:31 PM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > On Thu, 26 May 2011 17:23:20 -0700 > Ying Han <yinghan@xxxxxxxxxx> wrote: > >> On Thu, May 26, 2011 at 5:05 PM, KAMEZAWA Hiroyuki < >> kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >> >> > On Thu, 26 May 2011 14:07:49 -0700 >> > Ying Han <yinghan@xxxxxxxxxx> wrote: >> > >> > > This adds histogram to capture pagefault latencies on per-memcg basis. I >> > used >> > > this patch on the memcg background reclaim test, and figured there could >> > be more >> > > usecases to monitor/debug application performance. >> > > >> > > The histogram is composed 8 bucket in ns unit. The last one is infinite >> > (inf) >> > > which is everything beyond the last one. To be more flexible, the buckets >> > can >> > > be reset and also each bucket is configurable at runtime. >> > > >> > > memory.pgfault_histogram: exports the histogram on per-memcg basis and >> > also can >> > > be reset by echoing "reset". Meantime, all the buckets are writable by >> > echoing >> > > the range into the API. see the example below. >> > > >> > > /proc/sys/vm/pgfault_histogram: the global sysfs tunablecan be used to >> > turn >> > > on/off recording the histogram. >> > > >> > > Functional Test: >> > > Create a memcg with 10g hard_limit, running dd & allocate 8g anon page. >> > > Measure the anon page allocation latency. >> > > >> > > $ mkdir /dev/cgroup/memory/B >> > > $ echo 10g >/dev/cgroup/memory/B/memory.limit_in_bytes >> > > $ echo $$ >/dev/cgroup/memory/B/tasks >> > > $ dd if=/dev/zero of=/export/hdc3/dd/tf0 bs=1024 count=20971520 & >> > > $ allocate 8g anon pages >> > > >> > > $ echo 1 >/proc/sys/vm/pgfault_histogram >> > > >> > > $ cat /dev/cgroup/memory/B/memory.pgfault_histogram >> > > pgfault latency histogram (ns): >> > > < 600 2051273 >> > > < 1200 40859 >> > > < 2400 4004 >> > > < 4800 1605 >> > > < 9600 170 >> > > < 19200 82 >> > > < 38400 6 >> > > < inf 0 >> > > >> > > $ echo reset >/dev/cgroup/memory/B/memory.pgfault_histogram >> > > $ cat /dev/cgroup/memory/B/memory.pgfault_histogram >> > > pgfault latency histogram (ns): >> > > < 600 0 >> > > < 1200 0 >> > > < 2400 0 >> > > < 4800 0 >> > > < 9600 0 >> > > < 19200 0 >> > > < 38400 0 >> > > < inf 0 >> > > >> > > $ echo 500 520 540 580 600 1000 5000 >> > >/dev/cgroup/memory/B/memory.pgfault_histogram >> > > $ cat /dev/cgroup/memory/B/memory.pgfault_histogram >> > > pgfault latency histogram (ns): >> > > < 500 50 >> > > < 520 151 >> > > < 540 3715 >> > > < 580 1859812 >> > > < 600 202241 >> > > < 1000 25394 >> > > < 5000 5875 >> > > < inf 186 >> > > >> > > Performance Test: >> > > I ran through the PageFaultTest (pft) benchmark to measure the overhead >> > of >> > > recording the histogram. There is no overhead observed on both >> > "flt/cpu/s" >> > > and "fault/wsec". >> > > >> > > $ mkdir /dev/cgroup/memory/A >> > > $ echo 16g >/dev/cgroup/memory/A/memory.limit_in_bytes >> > > $ echo $$ >/dev/cgroup/memory/A/tasks >> > > $ ./pft -m 15g -t 8 -T a >> > > >> > > Result: >> > > "fault/wsec" >> > > >> > > $ ./ministat no_histogram histogram >> > > x no_histogram >> > > + histogram >> > > >> > +--------------------------------------------------------------------------+ >> > > N Min Max Median Avg >> > Stddev >> > > x 5 813404.51 824574.98 821661.3 820470.83 >> > 4202.0758 >> > > + 5 821228.91 825894.66 822874.65 823374.15 >> > 1787.9355 >> > > >> > > "flt/cpu/s" >> > > >> > > $ ./ministat no_histogram histogram >> > > x no_histogram >> > > + histogram >> > > >> > +--------------------------------------------------------------------------+ >> > > N Min Max Median Avg >> > Stddev >> > > x 5 104951.93 106173.13 105142.73 105349.2 >> > 513.78158 >> > > + 5 104697.67 105416.1 104943.52 104973.77 >> > 269.24781 >> > > No difference proven at 95.0% confidence >> > > >> > > Signed-off-by: Ying Han <yinghan@xxxxxxxxxx> >> > >> > Hmm, interesting....but isn't it very very very complicated interface ? >> > Could you make this for 'perf' ? Then, everyone (including someone who >> > don't use memcg) >> > will be happy. >> > >> >> Thank you for looking at it. >> >> There is only one per-memcg API added which is basically exporting the >> histogram. The "reset" and reconfiguring the bucket is not "must" but make >> it more flexible. Also, the sysfs API can be reduced if necessary since >> there is no over-head observed by always turning it on anyway. >> >> I am not familiar w/ perf, any suggestions how it is supposed to be look >> like? >> >> Thanks >> > > IIUC, you can record "all" latency information by perf record. Then, latency > information can be dumped out to some file. > > You can add a python? script for perf as > > # perf report memory-reclaim-latency-histgram -f perf.data > -o 500,1000,1500,2000..... > ...show histgram in text.. or report the histgram in graphic. > > Good point is > - you can reuse perf.data and show histgram from another point of view. > > - you can show another cut of view, for example, I think you can write a > parser to show "changes in hisgram by time", easily. > You may able to generate a movie ;) > > - Now, perf cgroup is supported. Then, > - you can see per task histgram > - you can see per cgroup histgram > - you can see per system-wide histgram > (If you record latency of usual kswapd/alloc_pages) > > - If you record latency within shrink_zone(), you can show per-zone > reclaim latency histgram. record parsers can gather them and > show histgram. This will be benefical to cpuset users. > > > I'm sorry if I miss something. After study a bit on perf, it is not feasible in this casecase. The cpu & memory overhead of perf is overwhelming.... Each page fault will generate a record in the buffer and how many data we can record in the buffer, and how many data will be processed later.. Most of the data that is recorded by the general perf framework is not needed here. On the other hand, the memory consumption is very little in this patch. We only need to keep a counter of each bucket and the recording can go on as long as the machine is up. As also measured, there is no overhead of the data collection :) So, the perf is not an option for this purpose. --Ying > > Thanks, > -Kame > > > > > > > > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href