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Date: Mon, 18 Sep 2017 10:57:08 +0200 From: Jiri Olsa <jolsa@...hat.com> To: kan.liang@...el.com Cc: acme@...nel.org, peterz@...radead.org, mingo@...hat.com, linux-kernel@...r.kernel.org, jolsa@...nel.org, namhyung@...nel.org, adrian.hunter@...el.com, lukasz.odzioba@...el.com, ak@...ux.intel.com Subject: Re: [PATCH RFC V2 00/10] perf top optimization On Sun, Sep 10, 2017 at 07:23:13PM -0700, kan.liang@...el.com wrote: > From: Kan Liang <kan.liang@...el.com> > > The patch series intends to fix the severe performance issue in > Knights Landing/Mill, when monitoring in heavy load system. > perf top costs a few minutes to show the result, which is > unacceptable. > With the patch series applied, the latency will reduces to > several seconds. > > machine__synthesize_threads and perf_top__mmap_read costs most of > the perf top time (> 99%). looks like this patchset adds locking into code paths used by other single threaded tools and that might be bad for them as noted by Andi in here: https://marc.info/?l=linux-kernel&m=149031672928989&w=2 he proposed solution and it was changed&posted by Arnaldo in here: https://marc.info/?l=linux-kernel&m=149132267410294&w=2 but looks like it never got merged could you please add this or similar code before you add the locking code/overhead in? thanks, jirka
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