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

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Date:	Mon, 25 Jun 2007 19:12:10 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.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>,
	"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 0/6] Convert all tasklets to workqueues

On 6/25/07, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Mon, 2007-06-25 at 18:46 -0700, Dan Williams wrote:
> >
> > Context switches on this platform flush the L1 cache so bouncing
> > between a workqueue and the MD thread is painful.
>
> Why is context switches between two kernel threads flushing the L1
> cache?  Is this a flaw in the ARM arch?  I would think the only thing
> that needs to be done between a context switch of two kernel threads (or
> even a user thread to a kernel thread) is update the general regs and
> stack. The memory access (page_tables or whatever ARM uses) should stay
> the same.
>
Yes you are right, ARM does not flush L1 when prev==next in switch_mm.

> Perhaps something else is at fault here.
>
I'll try and dig a bit deeper...
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