linux-kernel - Re: [patch 06/11] syslets: core, documentation

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Message-ID: <20070214203438.GL32271@kvack.org>
Date:	Wed, 14 Feb 2007 15:34:38 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Russell King <rmk+lkml@....linux.org.uk>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 06/11] syslets: core, documentation

On Wed, Feb 14, 2007 at 12:14:29PM -0800, Davide Libenzi wrote:
> I think you may have mis-interpreted my words. *When* a schedule would 
> block a synco execution try, then you do have a context switch. Noone 
> argue that, and the code is clear. The sys_async_exec thread will block, 
> and a newly woke up thread will re-emerge to sys_async_exec with a NULL 
> returned to userspace. But in a "cachehit" case (no schedule happens 
> during the syscall/*let execution), there is no context switch at all. 
> That is the whole point of the optimization.

And I will repeat myself: that cannot be done.  Tell me how the following 
what if scenario works: you're in an MMX optimized memory copy and you take 
a page fault.  How does returning to the submittor of the async operation 
get the correct MMX state restored?  It doesn't.

		-ben
-- 
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