Messages in this thread | | | Date | Wed, 20 Jan 2010 08:49:46 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/2] perf tools: Cope with sparsely-numbered CPUs |
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* Anton Blanchard <anton@samba.org> wrote:
> > Hi Ingo, > > > > For system-wide monitoring, the perf tools currently ask how many CPUs are > > > online, and then instantiate perf_events for CPUs 0 ... N-1. This doesn't > > > work correctly when CPUs are numbered sparsely. For example, a four-core > > > POWER6 in single-thread mode will have CPUs 0, 2, 4 and 6. The perf tools > > > will try to open counters on CPUs 0, 1, 2 and 3, and either fail with an > > > error message or silently ignore CPUs 4 and 6. > > > > > > This fixes the problem by making perf stat, perf record and perf top > > > create counters for increasing CPU numbers until they have a counter > > > for each online CPU. If the attempt to create a counter on a given > > > CPU fails, we get an ENODEV error and we just move on to the next CPU. > > > To avoid an infinite loop in case the number of online CPUs gets > > > reduced while we are creating counters, we re-read the number of > > > online CPUs when we fail to create a counter on some CPU. > > > > > > Reported-by: Michael Neuling <mikey@neuling.org> > > > Tested-by: Michael Neuling <mikey@neuling.org> > > > Cc: stable@kernel.org > > > Signed-off-by: Paul Mackerras <paulus@samba.org> > > > --- > > > tools/perf/builtin-record.c | 36 ++++++++++++++++++++++++++++-------- > > > tools/perf/builtin-stat.c | 15 +++++++++++++-- > > > tools/perf/builtin-top.c | 27 +++++++++++++++++++-------- > > > 3 files changed, 60 insertions(+), 18 deletions(-) > > > > nice fix! > > > > The linecount bloat is a bit worrying though. I'm wondering, since we have 3 > > loops now (and possibly more upcoming), wouldnt it be a cleaner fix to have > > some generic idiom of 'loop through all online cpus' somewhere in lib/*.c? > > > > This would work better in the long run than spreading all the sysconf calls > > and special cases across all those callsites. (new tools will inevitably get > > it wrong as well) > > > > As a practical matter we can commit your fix and do the cleanup/consolidation > > as a separate patch, to not hold up your fix (and to help fix/bisect any > > problems that would happen due to the consolidation) - as long as a > > consolidation patch is forthcoming as well. > > It looks like this hasn't made it to mainline. Any chance we could get it in > and look at a cleanup post 2.6.33?
Sure, if they come together we can apply one to an urgent branch and the other to a .34 branch.
Ingo
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