linux-kernel - Re: [RFC PATCH 6/6] Convert tasklets to work queues

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Message-Id: <200706231315.27426.arnd@arndb.de>
Date:	Sat, 23 Jun 2007 13:15:26 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	john stultz <johnstul@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, kuznet@....inr.ac.ru
Subject: Re: [RFC PATCH 6/6] Convert tasklets to work queues

On Friday 22 June 2007, Steven Rostedt wrote:
> This patch creates an alternative for drivers from using tasklets.
> It creates a "work_tasklet". When configured to use work_tasklets
> instead of tasklets, instead of creating tasklets, a work queue
> is made in its place.  The API is still the same, and the drivers
> don't know that a work queue is being used.
> 

Perhaps the API can be slimmed down in the process, because half
of the tasklet interface functions are hardly used at all.

> +#define DECLARE_TASKLET(name, func, data)				\
> +	struct tasklet_struct name = {					\
> +		__WORK_INITIALIZER((name).work, work_tasklet_exec),	\
> +		LIST_HEAD_INIT((name).list),				\
> +		0,							\
> +		ATOMIC_INIT(0),						\
> +		func,							\
> +		data,							\
> +		#name							\
> +	}

18 users of this macro. Maybe too much for the start, but if we convert
all of them to use either tasklet_init or use work queues directly,
the macro can go away.

> +#define DECLARE_TASKLET_DISABLED(name, func, data)			\
> +	struct tasklet_struct name = {					\
> +		__WORK_INITIALIZER((name).work, work_tasklet_exec),	\
> +		LIST_HEAD_INIT((name).list),				\
> +		0,							\
> +		ATOMIC_INIT(1),						\
> +		func,							\
> +		data,							\
> + 		#name							\
> +	}

this one is easier, there are only four users in total: three input
drivers, and tipc.

> +void tasklet_schedule(struct tasklet_struct *t);
> +#define tasklet_hi_schedule tasklet_schedule
> +extern fastcall void tasklet_enable(struct tasklet_struct *t);
> +#define tasklet_hi_enable tasklet_enable

there are 34 files using tasklet_hi_* functions. In theory, these
could be converted to the non-hi version with a simple search and
replace, if it's clear that there is not much point in keeping them.

The most common use of tasklet_hi is in the alsa drivers. If it
actually makes a difference for them already, maybe there should
be an alsa softirq instead of moving them all over to work queues.

> +void tasklet_disable_nosync(struct tasklet_struct *t);

only has two users, bcm43xx and sc92031. If both are
converted to workqueue, the interface removed can be
removed.

> +extern void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu);

only one user in total, rcupdate.c. You already take care of that,
it seems the declaration is just a leftover.

	Arnd <><
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