Messages in this thread | | | From | Arnaldo Carvalho de Melo <> | Date | Tue, 21 Apr 2020 12:59:46 -0300 | Subject | Re: kernel/perf: Sample data being lost |
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Em Tue, Apr 21, 2020 at 05:54:29PM +0200, Thomas Richter escreveu: > Since a couple of days I see this warning popping up very often: > > [root@m35lp76 perf]# ./perf record --call-graph dwarf -e rb0000 -- find / > [ perf record: Woken up 282 times to write data ] > Warning: > Processed 16999 events and lost 382 chunks! > > Check IO/CPU overload! > > [ perf record: Captured and wrote 125.730 MB perf.data (16219 samples) ] > [root@m35lp76 perf]# > > The machine is idle, its my development system, so not much going on. > It also happens using a software event, for example cycles. It shows > up more often, the larger the sample size is. So for example: > > [root@m35lp76 perf]# pwd > /root/linux/tools/perf > [root@m35lp76 perf]# ./perf record --call-graph dwarf -- find > [ perf record: Woken up 2 times to write data ] > Warning: > Processed 231 events and lost 7 chunks! > > Check IO/CPU overload! > > [ perf record: Captured and wrote 1.000 MB perf.data (130 samples) ] > [root@m35lp76 perf]# > > I have very seldom observed this before, only in extremely rare cases with > a heavily loaded machine. I am wondering what has changed, I haven't > changed anything in the s390 PMU device drivers. > It could be > - common kernel code when writing into the ringbuffer. > - the perf tool too slow to read data from the mapped buffer. > However I have not come across changes in this area. > > Has anybody observed similar issue? > > PS: I have added some printk messages into my PMU devices drivers. > I have seen messages that the 16384 pages for auxilary buffers are full > and that samples have been dropped.
Can you try to bisect tools/perf?
Something like:
git checkout v5.4
build it, no problems? Use it as the 'git bisect good' starting point.
- Arnaldo
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