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

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Message-ID: <20080813111635.657febc0@infradead.org>
Date:	Wed, 13 Aug 2008 11:16:35 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, 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,
	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?

On Wed, 13 Aug 2008 11:04:29 -0700
Ulrich Drepper <drepper@...hat.com> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Linus Torvalds wrote:
> > Ulrich, I don't understand why you worry more about a _potential_
> > (and fairly unlikely) complaint, than about a real one today.
> 
> Of course I care.  All I try to do is to prevent going from one
> extreme (all focus on P4s) to the other (ignore P4s completely).

(fwiw as far as I know this is only about early 64 bit P4s, not later
generations)
> 
> Even ignoring this one case here, I think it's in any case useful for
> userlevel to tell the kernel that an anonymous memory region is needed
> for a stack.  This might allow better optimizations and/or security
> implementations.

yeah maybe we should also tell it we expect it to be used downwards.
Oh wait.. MAP_GROWSDOWN ?

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