Messages in this thread | | | Date | Thu, 17 Oct 2013 09:59:28 -0600 | From | David Ahern <> | Subject | Re: [PATCH v2] perf: disable PERF_RECORD_MMAP2 support |
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On 10/17/13 9:57 AM, Stephane Eranian wrote: > On Thu, Oct 17, 2013 at 5:54 PM, David Ahern <dsahern@gmail.com> wrote: >> On 10/17/13 8:28 AM, Stephane Eranian wrote: >>> >>> >>> For now, we disable the extended MMAP record support (MMAP2). >>> We have identified cases where it would not report the correct >>> mapping information, clone(VM_CLONE) but with separate pids. >>> We will revisit the support once we find a solution for this case. >>> >>> The patch changes the kernel to return EINVAL if attr->mmap2 >>> is set. The patch also modifies the perf tool to use regular >>> PERF_RECORD_MMAP >>> for synthetic events and it also prevents the tool from requesting >>> attr->mmap2 >>> mode because the kernel would reject it. >>> >>> The support will be revisited once the kenrel interface is updated. >> >> >> Why not disable mmap2 as well: >> >> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c >> index 0ce9febf1ba0..289f34dbe970 100644 >> --- a/tools/perf/util/evsel.c >> +++ b/tools/perf/util/evsel.c >> @@ -678,7 +678,7 @@ void perf_evsel__config(struct perf_evsel *evsel, >> attr->sample_type |= PERF_SAMPLE_WEIGHT; >> >> attr->mmap = track; >> - attr->mmap2 = track && !perf_missing_features.mmap2; >> + /* attr->mmap2 = track && !perf_missing_features.mmap2; */ >> attr->comm = track; >> > It is disabled automatically later on. I checked that. Wanted to minimize > the changes. >
Understood that the fallback kicks in. Why fail the perf_event_open every single time when we know it is not going to succeed?
David
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