linux-kernel - Re: [PATCH 1/2] perf ftrace: Check min/max latency only with bucket range

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Message-ID: <Z4EonTmShlWn3n0X@x1>
Date: Fri, 10 Jan 2025 11:03:09 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 1/2] perf ftrace: Check min/max latency only with bucket
 range

On Fri, Jan 10, 2025 at 10:09:14AM +0000, Gabriele Monaco wrote:
> 2025-01-10T00:46:49Z Namhyung Kim <namhyung@...nel.org>:
> 
> > On Thu, Jan 09, 2025 at 08:53:02AM +0100, Gabriele Monaco wrote:
> >> On Wed, 2025-01-08 at 13:00 -0800, Namhyung Kim wrote:
> >>> It's an optional feature and remains 0 when bucket range is not
> >>> given.
> >>> And it makes the histogram goes to the last entry always because any
> >>> latency (num) is greater than or equal to 0.
> >>
> >> Thanks Namhyung for fixing this, something definitely slipped while
> >> testing..
> >>
> >> I confirm your patches work well also when the bucket range is provided but the
> >> min latency isn't.
> >>
> >> I'm wondering if it would be cleaner to propagate your changes (using
> >> min/max latency only if bucket_range is provided) also to
> >> make_histogram. That function currently works since we assume
> >> min_latency to be always 0, which is the case but probably not
> >> considering it altogether would look a bit better and prevent some
> >> headache in the future.
> >
> > It looks good.  One thing I concern is 'num += min_latency' before
> > do_inc.  I put it there to make it symmetric to 'num -= min_latency'
> > so it should go to inside the block too.
> >
> > Or you could factor it out as a function like 'i = get_bucket_index(num)'
> > so that it can keep the original num for the stats.
> >
> 
> Good point, I can have a deeper look at that. But I'd say it can come as a cleanup patch later.
> I have a couple more changes in mind and this would be no longer related to your changes.

I'm tentatively taking this as an:

Acked-by: Gabriele Monaco <gmonaco@...hat.com>

But it would be great to have it as a Reviewed-by and perhaps a
Tested-by, provided explicitely in response to this thread, ok?

Thanks,

- Arnaldo