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

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Date:	Wed, 13 Aug 2008 08:55:26 -0700
From:	Ulrich Drepper <drepper@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	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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Ingo Molnar wrote:
> Btw., can you see any problems with option #1: simply removing MAP_32BIT 
> from 64-bit stack allocations in glibc unconditionally?

Yes, as we both agree, there are still such machines out there.

The real problem is: what to do if somebody complains?  If we would have
the extra flag such people could be accommodated.  If there is no such
flag then distributions cannot just add the flag (it's part of the
kernel API) and they would be caught between a rock and a hard place.
Option #2 provides the biggest flexibility.

I upstream kernel truly doesn't care about such machines anymore there
are two options:

- - really do nothing at all

- - at least reserve a flag in case somebody wants/has to implement option
  #2

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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