linux-kernel - Re: pthread_create() slow for many threads; also time to revisit 64b context switch optimization?

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Message-ID: <48A5B943.1010607@gmail.com>
Date:	Fri, 15 Aug 2008 10:13:39 -0700
From:	Ulrich Drepper <drepper@...il.com>
To:	Jamie Lokier <jamie@...reable.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	akpm@...ux-foundation.org, hugh@...itas.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, briangrant@...gle.com,
	cgd@...gle.com, mbligh@...gle.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: pthread_create() slow for many threads; also time to revisit
 64b context switch optimization?

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Jamie Lokier wrote:
> Suggest:
> 
> +#define MAP_STACK       0x20000         /* 31bit or 64bit address for stack, */
> +                                        /* whichever is faster on this CPU */

I agree.  Except for the comment.


> Also, is this _only_ useful for thread stacks, or are there other
> memory allocations where 31-bitness affects execution speed on old P4s?

Actually, I would define the flag as "do whatever is best assuming the
allocation is used for stacks".

For instance, minimally the /proc/*/maps output could show "[user
stack]" or something like this.  For security, perhaps, setting of
PROC_EXEC can be prevented.
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