From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70])
	by kanga.kvack.org (Postfix) with ESMTP id DA8496B02C1
	for <linux-mm@kvack.org>; Wed, 25 Jul 2018 10:28:07 -0400 (EDT)
Received: by mail-wr1-f70.google.com with SMTP id q18-v6so4258532wrr.12
        for <linux-mm@kvack.org>; Wed, 25 Jul 2018 07:28:07 -0700 (PDT)
Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65])
        by mx.google.com with SMTPS id y2-v6sor1244008wmg.19.2018.07.25.07.28.06
        for <linux-mm@kvack.org>
        (Google Transport Security);
        Wed, 25 Jul 2018 07:28:06 -0700 (PDT)
MIME-Version: 1.0
References: <20180724224635.143944-1-shakeelb@google.com> <CAOm-9arFu63A9YJ6yVtm6_LdtbRKZg1Q3dz8WugdkBBQfoOWYw@mail.gmail.com>
In-Reply-To: <CAOm-9arFu63A9YJ6yVtm6_LdtbRKZg1Q3dz8WugdkBBQfoOWYw@mail.gmail.com>
From: Shakeel Butt <shakeelb@google.com>
Date: Wed, 25 Jul 2018 07:27:50 -0700
Message-ID: <CALvZod7Fqj_pJ2sn+XiDsoDX4jBLM22iGUrB9PeJXg+8S5xExQ@mail.gmail.com>
Subject: Re: [PATCH] memcg: reduce memcg tree traversals for stats collection
Content-Type: text/plain; charset="UTF-8"
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: bmerry@ska.ac.za
Cc: Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, Vladimir Davydov <vdavydov.dev@gmail.com>, Greg Thelen <gthelen@google.com>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>, Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>

On Wed, Jul 25, 2018 at 4:26 AM Bruce Merry <bmerry@ska.ac.za> wrote:
>
> On 25 July 2018 at 00:46, Shakeel Butt <shakeelb@google.com> wrote:
> > I ran a simple benchmark which reads the root_mem_cgroup's stat file
> > 1000 times in the presense of 2500 memcgs on cgroup-v1. The results are:
> >
> > Without the patch:
> > $ time ./read-root-stat-1000-times
> >
> > real    0m1.663s
> > user    0m0.000s
> > sys     0m1.660s
> >
> > With the patch:
> > $ time ./read-root-stat-1000-times
> >
> > real    0m0.468s
> > user    0m0.000s
> > sys     0m0.467s
>
> Thanks for cc'ing me. I've tried this patch using my test case and the
> results are interesting. With the patch applied, running my script
> only generates about 8000 new cgroups, compared to 40,000 before -
> presumably because the optimisation has altered the timing.
>
> On the other hand, if I run the script 5 times to generate 40000
> zombie cgroups, the time to get stats for the root cgroup (cgroup-v1)
> is almost unchanged at around 18ms (was 20ms, but there were slightly
> more cgroups as well), compared to the almost 4x speedup you're seeing
> in your test.
>

Hi Bruce, I think your script is trying to create zombies, so, the
experiments after that script will be non-deterministic. Why not just
create 40k cgroups ,no need for zombies, and the see how much this
patch affects reading stats.

Shakeel