Message-ID: <565F3CFF.8050102@hpe.com>
Date: Wed, 02 Dec 2015 13:48:31 -0500
From: Waiman Long <waiman.long@hpe.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>, Paul Turner <pjt@google.com>,
        Ben Segall <bsegall@google.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Yuyang Du <yuyang.du@intel.com>
Subject: Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers
 and writers of load_avg
References: <1448478580-26467-1-git-send-email-Waiman.Long@hpe.com> <1448478580-26467-4-git-send-email-Waiman.Long@hpe.com> <20151130102240.GH17308@twins.programming.kicks-ass.net> <565C9FDC.9020603@hpe.com> <20151130220953.GD3816@twins.programming.kicks-ass.net> <565D1A16.7080105@hpe.com> <20151201084944.GK3816@twins.programming.kicks-ass.net>
In-Reply-To: <20151201084944.GK3816@twins.programming.kicks-ass.net>
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On 12/01/2015 03:49 AM, Peter Zijlstra wrote:
> On Mon, Nov 30, 2015 at 10:55:02PM -0500, Waiman Long wrote:
>> On 11/30/2015 05:09 PM, Peter Zijlstra wrote:
>>> On Mon, Nov 30, 2015 at 02:13:32PM -0500, Waiman Long wrote:
>>>>> This begs the question tough; why are you running a global load in a
>>>>> cgroup; and do we really need to update this for the root cgroup? It
>>>>> seems to me we don't need calc_tg_weight() for the root cgroup, it
>>>>> doesn't need to normalize its weight numbers.
>>>>>
>>>>> That is; isn't this simply a problem we should avoid?
>>>> I didn't use any cgroup in my test setup. Autogroup was enabled, though.
>>>> Booting up a 4.4-rc2 kernel caused sched_create_group() to be called 56
>>>> times.
>>> Yeah, can you kill autogroup and see if that helps? If not, we probably
>>> should add some code to avoid calculating things for the root group.
>> I will try that out tomorrow. However, SCHED_AUTOGROUP was enabled in the
>> distribution kernels. So we still need to look at that with autogroup
>> enabled.
> Meh, or just tell the people that have stupid large machines to use
> noautogroup on boot (its of questionable benefit in the first place imo,
> esp. on servers).

Yes, I was able to recover most of the lost performance by disabling 
autogroup. I did send out a new patch to disable load_avg update for 
root_task_group. I need that for backporting to earlier kernels which 
was forced to update load_avg for every clock tick even for root_task_group.

Cheers,
Longman
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