linux-kernel - Re: [PATCH 2/3] bcache: Convert to lib/time

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Date:   Wed, 31 Aug 2022 13:36:39 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Coly Li <colyli@...e.de>
Cc:     linux-kernel@...r.kernel.org, linux-bcache@...r.kernel.org
Subject: Re: [PATCH 2/3] bcache: Convert to lib/time_stats

On Thu, Sep 01, 2022 at 01:02:37AM +0800, Coly Li wrote:
> Can I understand that rate = 1/frequency ?  Then frequency 4 is around to rate 0.

Correct, rate = 1/frequency.

> > The quantiles are for the duration, they give you an idea of the statistical
> > distribution, see https://en.wikipedia.org/wiki/Quantile
> 
> I wanted to ask how to read the quantiles line. Does it mean that 1 ns is
> equally divided by 15 segments, and the counter values are for the divided
> 1/15 ns segments?

It is the 15 boundaries between 16 equal segments, yes.

> Quantiles are much humane, standard deviation is scared… Just FYI LOL.

That's valuable feedback then, maybe we'll keep both. The more expensive part of
time stats is just ingesting data points, but we've got a percpu buffer frontend
for that - just doing a bit more moth doesn't cost much.