linux-kernel - Re: [PATCH] Do not include throttled time as steal time

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Date:	Mon, 05 Dec 2011 17:20:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike wolf <mjw@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, paulmck <paulmck@...ux.vnet.ibm.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH] Do not include throttled time as steal time

On Mon, 2011-12-05 at 09:08 -0600, Mike wolf wrote:

Hi Mike, couple of problems with this:

1) You failed to CC the appropriate maintainers for the piece of code
you're trying to have changed. When in doubt see the MAINTAINERS
file ;-)

2) You failed to CC the people who wrote the feature you're having a
problem with.

> When the linux kernel is running as the guest OS and is configured
> for bandwidth control and steal time reporting, it can be confusing
> to users to see the throttled time show up in the steal time stats.
> The user will think they are not getting the cpu resources they have
> been configured.

Supposedly this is a BAD (tm) thing :-)

> Signed-off-by: Mike Wolf <mjw@...ux.vnet.ibm.com>
> ---
>   kernel/sched_fair.c  |    4 ++--
>   kernel/sched_stats.h |    7 ++++++-
>   2 files changed, 8 insertions(+), 3 deletions(-)

3) You blink you loose, those files don't exist anymore. Patches are
best provided against the development tree of the particular subsystem
you're working against.

In this particular case tip/master is your target.

>   static inline void sched_info_depart(struct task_struct *t)
>   {
> +    struct task_group *tg = task_group(t);
> +    struct cfs_rq *cfs_rq;
>       unsigned long long delta = task_rq(t)->clock -
>                       t->sched_info.last_arrival;
> 
> +    cfs_rq = tg->cfs_rq[smp_processor_id()];
>       rq_sched_info_depart(task_rq(t), delta);
> 
> -    if (t->state == TASK_RUNNING)
> +
> +    if (t->state == TASK_RUNNING && !throttled_hierarchy(cfs_rq))
>           sched_info_queued(t);
>   }

4) so there's a lot more steal time crap all over the scheduler, you
failed to explain why only this particular bit is important enough to
change.



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