Messages in this thread | | | Subject | Re: [PATCH 2/2] perf: Mmap 512 kiB by default | From | Peter Zijlstra <> | Date | Thu, 31 Mar 2011 10:09:52 +0200 |
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On Thu, 2011-03-31 at 03:35 +0200, Frederic Weisbecker wrote: > The default setting of perf record is to mmap 128 pages if the user > did not override with -m. > However the page size may vary accross different architecture > settings, giving different default size between each. > > Moreover the kernel side still has a default max number of mlocked > pages of 512 kiB + 1 page for unprivileged users. 128 + 1 pages > with page size > 4096 overlaps this threshold. > > Thus, better adapt to this limitation and set the default number of > pages to fit those 512 kiB + 1 page. > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Ingo Molnar <mingo@elte.hu> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > Cc: Paul Mackerras <paulus@samba.org> > Cc: Stephane Eranian <eranian@google.com> > --- > tools/perf/builtin-record.c | 6 +++++- > 1 files changed, 5 insertions(+), 1 deletions(-) > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index 6febcc1..a7e14bd 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -41,7 +41,7 @@ static u64 user_interval = ULLONG_MAX; > static u64 default_interval = 0; > > static unsigned int page_size; > -static unsigned int mmap_pages = 128; > +static unsigned int mmap_pages = UINT_MAX; > static unsigned int user_freq = UINT_MAX; > static int freq = 1000; > static int output; > @@ -506,6 +506,10 @@ static int __cmd_record(int argc, const char **argv) > if (have_tracepoints(&evsel_list->entries)) > perf_header__set_feat(&session->header, HEADER_TRACE_INFO); > > + /* 512 kiB: default amount of unprivileged mlocked memory */ > + if (mmap_pages == UINT_MAX) > + mmap_pages = (512 * 1024) / page_size; > + > if (forks) { > child_pid = fork(); > if (child_pid < 0) {
Ok, these two patches look good, I'll queue them. However a follow up might be to change the perf-record parameter from nr_pages to kb, which is a much more user friendly interface anyway ;-)
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