linux-kernel - Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

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Date:	Fri, 29 Jun 2007 20:52:47 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
Cc:	Ingo Molnar <mingo@...e.hu>, Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	john stultz <johnstul@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, matthew.wilcox@...com
Subject: Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

On 06/29, Alexey Kuznetsov wrote:
> 
> > If I understand correctly, this is because tasklet_head.list is protected
> > by local_irq_save(), and t could be scheduled on another CPU, so we just
> > can't steal it, yes?
> 
> Yes. All that code is written to avoid synchronization as much as possible.

Thanks!

> 
> > If we use worqueues, we can change the semantics of tasklet_kill() so
> > that it really cancels an already scheduled tasklet.
> > 
> > The question is: would it be the wrong/good change?
> 
> If it does not add another usec to tasklet_schedule(), it would be good.

No, it won't slowdown tasklet_schedule(). Instead it will speedup tasklet_kill.


Steven, unless you have some objections, could you change tasklet_kill() ?

> +static inline void tasklet_kill(struct tasklet_struct *t)
>  {
> -       return test_bit(TASKLET_STATE_SCHED, &t->state);
> +       flush_workqueue(ktaskletd_wq);
>  }

Just change flush_workqueue(ktaskletd_wq) to cancel_work_sync(t-work).

Oleg.

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