linux-kernel - Re: [tg_shares_up rewrite v2 10/11] sched: allow update_cfs

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Date:	Thu, 11 Nov 2010 03:13:00 -0800
From:	Paul Turner <pjt@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	mingo@...e.hu, vatsa@...ibm.com, cfriesen@...tel.com,
	svaidy@...ux.vnet.ibm.com, pbourdon@...ellency.fr,
	bharata@...ux.vnet.ibm.com, kmr@...ibm.com,
	balbir@...ux.vnet.ibm.com
Subject: Re: [tg_shares_up rewrite v2 10/11] sched: allow update_cfs_load to
 update global load

Ah, I should have checked that, sorry.

I've fixed these errors for a v3.  But in fixing them I've realized I
think we have a race in sched_destroy_group() (in patch 2/11).

While it's true that we are safe for a subsequent enqueue in the same
group, we're not protected against a list element being removed due to
decay in the update shares path.  Or from a another group being
enqueued (via wake-up).

Might as well fix this at the same time so I'll fix it and send out in
the morning.

Thanks!

On Wed, Nov 10, 2010 at 8:50 PM, David Miller <davem@...emloft.net> wrote:
> From: David Miller <davem@...emloft.net>
> Date: Wed, 10 Nov 2010 20:47:04 -0800 (PST)
>
>> From: Paul Turner <pjt@...gle.com>
>> Date: Wed, 10 Nov 2010 19:50:15 -0800
>>
>>> Refactor the global load updates from update_shares_cpu() so that
>>> update_cfs_load() can update global load when it is more than ~10% out of sync.
>>>
>>> The new global_load parameter allows us to force an update, regardless of
>>> the error factor so that we can synchronize w/ update_shares().
>>>
>>> Signed-off-by: Paul Turner <pjt@...gle.com>
>>
>> This patch breaks the build, you didn't update the arguments of
>> update_cfs_load() in the !CONFIG_FAIR_GROUP_SCHED case.
>
> And even with this fixed there are even larger problems, as you're
> making access to structure members such as 'load_unacc_exec_time'
> which only exist when CONFIG_FAIR_GROUP_SCHED is set, but you're doing
> it in code that is built unconditionally.
>
> Please fix all of these build problems, as I want to test your changes
> without all of the group scheduler bloat turned on.
>
> Thanks.
>
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