From 4e303fbe2d95806c875f5ebfcb3d980e20b4bd83 Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Fri, 26 Oct 2018 15:55:23 -0300 Subject: perf top: Allow disabling the overwrite mode In ebebbf082357 ("perf top: Switch default mode to overwrite mode") we forgot to leave a way to disable that new default, add a --overwrite option that can be disabled using --no-overwrite, since the code already in such a way that we can readily disable this mode. This is useful when investigating bugs with this mode like the recent report from David Miller where lots of unknown symbols appear due to disabling the events while processing them which disables all record types, not just PERF_RECORD_SAMPLE, which makes it impossible to resolve maps when we lose PERF_RECORD_MMAP records. This can be easily seen while building a kernel, when there are lots of short lived processes. Reported-by: David Miller Acked-by: Kan Liang Cc: Adrian Hunter Cc: Andi Kleen Cc: David Ahern Cc: Jin Yao Cc: Jiri Olsa Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Wang Nan Fixes: ebebbf082357 ("perf top: Switch default mode to overwrite mode") Link: https://lkml.kernel.org/n/tip-oqgsz2bq4kgrnnajrafcdhie@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/Documentation/perf-top.txt | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'tools/perf/Documentation') diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt index 114fda12aa49..d4be6061fe1c 100644 --- a/tools/perf/Documentation/perf-top.txt +++ b/tools/perf/Documentation/perf-top.txt @@ -242,6 +242,11 @@ Default is to monitor all CPUS. --hierarchy:: Enable hierarchy output. +--overwrite:: + This is the default, but for investigating problems with it or any other strange + behaviour like lots of unknown samples, we may want to disable this mode by using + --no-overwrite. + --force:: Don't do ownership validation. -- cgit v1.2.3