linux-kernel - Re: [PATCH 4/7] numa,sched: tracepoints for NUMA balancing active nodemask changes

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Date:	Mon, 20 Jan 2014 17:52:05 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	chegu_vinod@...com, mgorman@...e.de, mingo@...hat.com,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 4/7] numa,sched: tracepoints for NUMA balancing active
 nodemask changes

On Fri, Jan 17, 2014 at 04:12:06PM -0500, riel@...hat.com wrote:
> From: Rik van Riel <riel@...hat.com>
> 
> Being able to see how the active nodemask changes over time, and why,
> can be quite useful.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Chegu Vinod <chegu_vinod@...com>
> Signed-off-by: Rik van Riel <riel@...hat.com>
> ---
>  include/trace/events/sched.h | 34 ++++++++++++++++++++++++++++++++++
>  kernel/sched/fair.c          |  8 ++++++--
>  2 files changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index 67e1bbf..91726b6 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -530,6 +530,40 @@ TRACE_EVENT(sched_swap_numa,
>  			__entry->dst_pid, __entry->dst_tgid, __entry->dst_ngid,
>  			__entry->dst_cpu, __entry->dst_nid)
>  );
> +
> +TRACE_EVENT(update_numa_active_nodes_mask,

Please stick to the sched_ naming for these things.

Ideally we'd rename the sysctls too :/

> +++ b/kernel/sched/fair.c
> @@ -1300,10 +1300,14 @@ static void update_numa_active_node_mask(struct task_struct *p)
>  		faults = numa_group->faults_from[task_faults_idx(nid, 0)] +
>  			 numa_group->faults_from[task_faults_idx(nid, 1)];
>  		if (!node_isset(nid, numa_group->active_nodes)) {
> -			if (faults > max_faults * 4 / 10)
> +			if (faults > max_faults * 4 / 10) {
> +				trace_update_numa_active_nodes_mask(current->pid, numa_group->gid, nid, true, faults, max_faults);

While I think the tracepoint hookery is smart enough to avoid evaluating
arguments when they're disabled, it might be best to simply pass:
current and numa_group and do the dereference in fast_assign().

That said, this is the first and only numa tracepoint, I'm not sure why
this qualifies and other metrics do not.


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