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88b897a30c
This patch significantly improves the execution time of
perf_event__synthesize_mmap_events() when running perf record on systems
where processes have lots of threads.
It just happens that cat /proc/pid/maps support uses a O(N^2) algorithm to
generate each map line in the maps file. If you have 1000 threads, then you
have necessarily 1000 stacks. For each vma, you need to check if it
corresponds to a thread's stack. With a large number of threads, this can take
a very long time. I have seen latencies >> 10mn.
As of today, perf does not use the fact that a mapping is a stack, therefore we
can work around the issue by using /proc/pid/tasks/pid/maps. This entry does
not try to map a vma to stack and is thus much faster with no loss of
functonality.
The proc-map-timeout logic is kept in case users still want some upper limit.
In V2, we fix the file path from /proc/pid/tasks/pid/maps to actual
/proc/pid/task/pid/maps, tasks -> task. Thanks Arnaldo for catching this.
Committer note:
This problem seems to have been elliminated in the kernel since commit :
b18cb64ead ("fs/proc: Stop trying to report thread stacks").
Signed-off-by: Stephane Eranian <eranian@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170315135059.GC2177@redhat.com
Link: http://lkml.kernel.org/r/1489598233-25586-1-git-send-email-eranian@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.