linux-kernel - RE: [PATCH] sched: Folding nohz load accounting more accurate

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Message-ID: <000301cd49e8$1dbd2db0$59378910$@net>
Date:	Wed, 13 Jun 2012 21:41:50 -0700
From:	"Doug Smythies" <dsmythies@...us.net>
To:	"'Charles Wang'" <muming.wq@...il.com>
Cc:	"'Peter Zijlstra'" <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, "'Ingo Molnar'" <mingo@...hat.com>,
	"'Charles Wang'" <muming.wq@...bao.com>, "'Tao Ma'" <tm@....ma>,
	'含黛' <handai.szj@...bao.com>,
	"Doug Smythies" <dsmythies@...us.net>
Subject: RE: [PATCH] sched: Folding nohz load accounting more accurate

> On 2012.06.13 00:56 - 0700, Charles Wang wrote:

> Every cpu's load should be the load right on the time executing
> calculation.
> This is what my patch expected to do.

> After my patch, it's supposed to let every cpu's load calculation be
> independent from
> its idle and other cpus' influence when the calculation is finished.
> But it seems other problem exists.

> I recorded some trace, show as below:

Charles thanks for your detailed reply.
I am not sure I agree.

On purpose, I have left out your trace detail from this reply.
Why? Because I want to take a step back and answer a more fundamental
question first:
Is there (or was there) actually a problem that needed to be solved?

I am still not understanding what your expected reported load averages
for your 16 processes should be. How do you know that the 8 to 10 that
was being reported was incorrect?

I want to understand so that I can re-create your same reported load
averages are still to low situation on my test computer, before your patch.
Then show that it is fixed after your patch.
I have tried to re-create it and have been unsuccessful. Today, and since
you
showed at least 16 CPUs on your system, and I only have 8 CPUs, I tried with
8 processes at high duty cycle. The reported load average was always pretty
close to the actual load (see also attachment).

Perhaps I have some fundamental misunderstanding as to how reported load
averages should work. I have always used kernels compiled with
CONFIG_NO_HZ=no (tick based, rather than tickless) as the control reference.

View attachment "wang_high_load_example.txt" of type "text/plain" (3386 bytes)