Messages in this thread | | | From | Thomas Richter <> | Subject | kernel/perf: Sample data being lost | Date | Tue, 21 Apr 2020 17:54:29 +0200 |
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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.
Thanks a lot. -- Thomas Richter, Dept 3252, IBM s390 Linux Development, Boeblingen, Germany -- Vorsitzender des Aufsichtsrats: Matthias Hartmann Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
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