linux-kernel - Re: [patch] x86: split FPU state from task state

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Message-ID: <20070214220443.GN32271@kvack.org>
Date:	Wed, 14 Feb 2007 17:04:44 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Russell King <rmk+lkml@....linux.org.uk>,
	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] x86: split FPU state from task state

On Wed, Feb 14, 2007 at 10:49:44PM +0100, Ingo Molnar wrote:
> this can very much be done, with a straightforward extension of how we 
> handle FPU state. That makes sense independently of syslets/async as 
> well, so find below the standalone patch from Arjan. It's in my current 
> syslet queue and works great.

That patch adds a bunch of memory dereferences and another allocation 
to the thread creation code path -- a tax that all users must pay.  Granted, 
it's small, but at the very least should be configurable out for the 99.9% 
of users that will never use this functionality.

I'm willing to be convinced, it's just that I would like to see some 
numbers that scream out that this is a good thing.

		-ben
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