Messages in this thread | | | Date | Fri, 4 Mar 2022 16:39:24 +0100 | From | Peter Zijlstra <> | Subject | Re: [RESEND PATCH 2/2] perf/x86: improve the event scheduling to avoid unnecessary pmu_stop/start |
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On Fri, Mar 04, 2022 at 07:03:51PM +0800, Wen Yang wrote: > this issue has been there for a long time, we could reproduce it as follows:
What issue? You've not described an issue. So you cannot reference one.
This is still completely unreadable gibberish.
> 1, run a script that periodically collects perf data, eg: > while true > do > perf stat -e cache-misses,cache-misses,cache-misses -c 1 sleep 2 > perf stat -e cache-misses -c 1 sleep 2 > sleep 1 > done > > 2, run another one to capture the ipc, eg: > perf stat -e cycles:d,instructions:d -c 1 -i 1000
<snip line noise>
> the reason is that the nmi watchdog permanently consumes one fp > (*cycles*). therefore, when the above shell script obtains *cycles* > again, only one gp can be used, and its weight is 5. > but other events (like *cache-misses*) have a weight of 4, > so the counter used by *cycles* will often be taken away, as in > the raw data above: > [1] > n_events = 3 > assign = {33, 1, 32, ...} > --> > n_events = 6 > assign = {33, 3, 32, 0, 1, 2, ...}
Again unreadable... what do any of those numbers mean?
> > so it will cause unnecessary pmu_stop/start and also cause abnormal cpi.
How?!?
> Cloud servers usually continuously monitor the cpi data of some important > services. This issue affects performance and misleads monitoring. > > The current event scheduling algorithm is more than 10 years old: > commit 1da53e023029 ("perf_events, x86: Improve x86 event scheduling")
irrelevant
> we wish it could be optimized a bit.
I wish for a unicorn ...
> The fields msk_counters and msk_events are added to indicate currently > used counters and events so that the used ones can be skipped > in __perf_sched_find_counter and perf_sched_next_event functions to avoid > unnecessary pmu_stop/start.
Still not sure what your actual problem is, nor what the actual proposal is.
Why should I attempt to reverse engineer your code without basic understanding of what you're actually trying to achieve?
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