Messages in this thread | | | Date | Tue, 16 May 2017 10:42:25 -0700 | From | "Luck, Tony" <> | Subject | Re: [RFC] perf: Add "-f" and "-F" flags to watch a "/sys" style file |
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On Mon, May 15, 2017 at 09:45:58PM -0300, Arnaldo Carvalho de Melo wrote: > I haven't been following the discussion about the resctrl fs discussion > to understand why those values couldn't be read via > sys_perf_event_open(), so can't comment on that, but the implementation > on the tools/ classes look nice, i.e. -e will get perf_evsel instances > that interface with the kernel via sys_perf_event_open(), -f/-F will get > perf_evsel instances that read values via the rsctrl file system, clean.
It's kind of tortuous to connect the dots from these events to sys_perf_event_open(). That has a strong connection to a specific task, and/or a specific CPU. But these events count for a group of tasks and the resource is shared typically at the socket level.
E.g. we might have three "jobs" (each consisting of several processes/threads). We run them all in a shared restricted cache allocation environment, but wanto to measure how each is performing:
# cd /sys/fs/resctrl # mkdir cg1 # echo $$ > cg1/tasks # # echo "L3:0=ff000;1=ff000" > cg1/schemata # mkdir cg1/mon_tasks/j1 cg1/mon_tasks/j2 cg1/mon_tasks/j3 # # echo $$ > cg1/mon_tasks/j1/tasks # job1 & # echo $$ > cg1/mon_tasks/j2/tasks # job2 & # echo $$ > cg1/mon_tasks/j3/tasks # job3 &
Now we can view the cache occupancy for each of job1, job2, and job3 via some files[*] in each of these directories. Or see the summary cache occupancy for all three jobs via files in the control group (/sys/fs/resctrl/cg1) For me, I can easily see how to use "-f" options to look at the right files to get the information I want.
Offline we've talked at the white board level of either over-loading the "-G" flag used for Cgroups, or adding a new "-R" flag for resctrl groups and then having our internal kernel code respond to sys_perf_event_open() with a file descriptor that behaves like other "perf" file descriptors. Maybe someone will work out the syntax wrinkles to express that on the perf command line. Perhaps something like:
# perf stat -e intel/llc_occupancy -R /sys/fs/resctrl/cg1/mon_tasks/j1 ...
The "intel/llc_occupancy" event would need some special attributes so that perf would know that it requires "-R" option(s) too, and doesn't work with other options like "-C".
> P.S. I may be slow to reply because I'm on vacation till the end of this > month.
Thanks for looking at this while on vacation. Now exit e-mail and enjoy your time off :-)
-Tony
[*] exact names still in flux, and will probably change again when we post patches and people who are better at choosing names begin to review then.
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