Messages in this thread | | | Date | Sat, 9 May 2009 12:36:46 +0200 | From | Ingo Molnar <> | Subject | Re: [patch] tracing/mm: add page frame snapshot trace |
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* Wu Fengguang <fengguang.wu@intel.com> wrote:
> > Preliminary timings on an older, 1GB RAM 2 GHz Athlon64 box show > > that it's plenty fast: > > > > # time echo -1 > /debug/tracing/objects/mm/pages/trigger > > > > real 0m0.127s > > user 0m0.000s > > sys 0m0.126s > > > > # time cat /debug/tracing/per_cpu/*/trace_pipe_raw > /tmp/page-trace.bin > > > > real 0m0.065s > > user 0m0.001s > > sys 0m0.064s > > > > # ls -l /tmp/1 > > -rw-r--r-- 1 root root 13774848 2009-05-09 11:46 /tmp/page-dump.bin > > > > 127 millisecs to collect, 65 milliseconds to dump. (And that's not > > using splice() to dump the trace data.) > > That's pretty fast and on par with kpageflags!
It's already faster here than kpageflags, on a 32 GB box i just tried, and the sum of timings (dumping + reading of 4 million page frame records, into/from a sufficiently large trace buffer) is 2.8 seconds.
current upstream kpageflags is 3.3 seconds:
phoenix:/home/mingo> time cat /proc/kpageflags > /tmp/1
real 0m3.338s user 0m0.004s sys 0m0.608s
(although it varies around a bit, sometimes back to 3.0 secs, sometimes more)
That's about 10% faster. Note that output performance could be improved more by using splice().
Also, it's apples to oranges, in an unfavorable-to-ftrace way: the pages object collection outputs all of these fields:
field:unsigned short common_type; offset:0; size:2; field:unsigned char common_flags; offset:2; size:1; field:unsigned char common_preempt_count; offset:3; size:1; field:int common_pid; offset:4; size:4; field:int common_tgid; offset:8; size:4;
field:unsigned long pfn; offset:16; size:8; field:unsigned long flags; offset:24; size:8; field:unsigned long index; offset:32; size:8; field:unsigned int count; offset:40; size:4; field:unsigned int mapcount; offset:44; size:4;
plus it generates and outputs the timestamp as well - while kpageflags is just page flags. (and kpagecount is only page counts)
Spreading the dumping+output out to the 16 CPUs of this box would shorten the run time at least 10-fold, to about 0.3-0.5 seconds IMHO. (but that has to be tried and measured first)
Ingo
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