linux-kernel - Re: [PATCH 08/18] sched: Reschedule task on preferred NUMA node once selected

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Message-ID: <20130801044757.GA6151@linux.vnet.ibm.com>
Date:	Thu, 1 Aug 2013 10:17:57 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/18] sched: Reschedule task on preferred NUMA node once
 selected

* Mel Gorman <mgorman@...e.de> [2013-07-15 16:20:10]:

> A preferred node is selected based on the node the most NUMA hinting
> faults was incurred on. There is no guarantee that the task is running
> on that node at the time so this patch rescheules the task to run on
> the most idle CPU of the selected node when selected. This avoids
> waiting for the balancer to make a decision.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  kernel/sched/core.c  | 17 +++++++++++++++++
>  kernel/sched/fair.c  | 46 +++++++++++++++++++++++++++++++++++++++++++++-
>  kernel/sched/sched.h |  1 +
>  3 files changed, 63 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 5e02507..b67a102 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4856,6 +4856,23 @@ fail:
>  	return ret;
>  }
> 
> +#ifdef CONFIG_NUMA_BALANCING
> +/* Migrate current task p to target_cpu */
> +int migrate_task_to(struct task_struct *p, int target_cpu)
> +{
> +	struct migration_arg arg = { p, target_cpu };
> +	int curr_cpu = task_cpu(p);
> +
> +	if (curr_cpu == target_cpu)
> +		return 0;
> +
> +	if (!cpumask_test_cpu(target_cpu, tsk_cpus_allowed(p)))
> +		return -EINVAL;
> +
> +	return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);

As I had noted earlier, this upsets schedstats badly.
Can we add a TODO for this patch, which mentions that schedstats need to
taken care.

One alternative that I can think of is to have a per scheduling class
routine that gets called and does the needful.
for example: for fair share, it could update the schedstats as well as
check for cfs_throttling.

But I think its an issue that needs some fix or we should obsolete
schedstats.

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