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Date: Thu, 7 May 2020 22:43:43 -0700 From: Ian Rogers <irogers@...gle.com> To: Andi Kleen <ak@...ux.intel.com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, Andrii Nakryiko <andriin@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...omium.org>, Kajol Jain <kjain@...ux.ibm.com>, John Garry <john.garry@...wei.com>, Jin Yao <yao.jin@...ux.intel.com>, Kan Liang <kan.liang@...ux.intel.com>, Cong Wang <xiyou.wangcong@...il.com>, Kim Phillips <kim.phillips@....com>, LKML <linux-kernel@...r.kernel.org>, Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, linux-perf-users <linux-perf-users@...r.kernel.org>, Stephane Eranian <eranian@...gle.com> Subject: Re: [RFC PATCH 0/7] Share events between metrics On Thu, May 7, 2020 at 2:47 PM Andi Kleen <ak@...ux.intel.com> wrote: > > > > - without this change events within a metric may get scheduled > > > together, after they may appear as part of a larger group and be > > > multiplexed at different times, lowering accuracy - however, less > > > multiplexing may compensate for this. > > > > I agree the heuristic in this patch set is naive and would welcome to > > improve it from your toplev experience. I think this change is > > progress on TopDownL1 - would you agree? > > TopdownL1 in non SMT mode should always fit. Inside a group > deduping always makes sense. > > The problem is SMT mode where it doesn't fit. toplev tries > to group each node and each level together. Thanks Andi, I've provided some examples of TopDownL3_SMT in the cover letter of the v3 patch set: https://lore.kernel.org/lkml/20200508053629.210324-1-irogers@google.com/ I tested sandybridge and cascadelake and the results look similar to the non-SMT version. Let me know if there's a different variant to test. > > > > I'm wondering if what is needed are flags to control behavior. For > > example, avoiding the use of groups altogether. For TopDownL1 I see. > > Yes the current situation isn't great. > > For Topdown your patch clearly is an improvement, I'm not sure > it's for everything though. > > Probably the advanced heuristics are only useful for a few > formulas, most are very simple. So maybe it's ok. I guess > would need some testing over the existing formulas. Agreed, do you have a pointer on a metric group where things would obviously be worse? I started off with a cache miss and hit rate metric and similar to topdown this approach is a benefit. In v3 I've added a --metric-no-merge option to retain existing grouping behavior, I've also added a --metric-no-group that avoids groups for all metrics. This may be useful if the NMI watchdog can't be disabled. Thanks for the input! Ian > -Andi
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