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Date:   Thu, 7 May 2020 14:46:52 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     Ian Rogers <irogers@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Kajol Jain <kjain@linux.ibm.com>,
        John Garry <john.garry@huawei.com>,
        Jin Yao <yao.jin@linux.intel.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Kim Phillips <kim.phillips@amd.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        linux-perf-users <linux-perf-users@vger.kernel.org>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [RFC PATCH 0/7] Share events between metrics
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> > - 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.

> 
> 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.


-Andi