linux-kernel - Re: [PATCH] sched: Introduce TASK_NOLOAD and TASK

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Date:	Sat, 9 May 2015 11:49:01 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	neilb@...e.de
Subject: Re: [PATCH] sched: Introduce TASK_NOLOAD and TASK_IDLE


	Hello,

On Fri, 8 May 2015, Peter Zijlstra wrote:

> Subject: sched: Introduce TASK_NOLOAD and TASK_IDLE
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Fri May 8 14:23:45 CEST 2015
> 
> Currently people use TASK_INTERRUPTIBLE to idle kthreads and wait for
> 'work' because TASK_UNINTERRUPTIBLE contributes to the loadavg. Having
> all idle kthreads contribute to the loadavg is somewhat silly.
> 
> Now mostly this works OK, because kthreads have all their signals
> masked. However there's a few sites where this is causing problems and
> TASK_UNINTERRUPTIBLE should be used, except for that loadavg issue.
> 
> This patch adds TASK_NOLOAD which, when combined with
> TASK_UNINTERRUPTIBLE avoids the loadavg accounting.
> 
> As most of imagined usage sites are loops where a thread wants to
> idle, waiting for work, a helper TASK_IDLE is introduced.

	After checking our code in net/netfilter/ipvs/ip_vs_sync.c,
sync_thread_master(), we may also need some wrappers:

- schedule_timeout_idle (instead of schedule_timeout call):
	__set_current_state(TASK_IDLE);
	return schedule_timeout(timeout);

	- we here are really idle, so "N" looks ok

- pair of __wait_event_idle(wq, condition) and
	wait_event_idle(wq, condition) macros

	- we here are write-blocked for socket, not sure
	if this blocked vs idle difference is useful to
	represent, in new bit for this blocked state "B"=2048,
	with 2 TASK_NOLOAD variants: N(idle) and B(blocked,
	2|1024|2048, eg. for read-blocked or write-blocked).
	It will need additional argument 'state'/'blocked' for 
	*wait_event_idle().

Regards

--
Julian Anastasov <ja@....bg>
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