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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: David McCullough <davidm@snapgear.com>
Cc: Bernardo Innocenti <bernie@develer.com>,
	Christoph Hellwig <hch@infradead.org>,
	"David S. Miller" <davem@redhat.com>,
	uclinux-dev@uclinux.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Greg Ungerer <gerg@snapgear.com>
Subject: Re: [uClinux-dev] Kernel 2.6 size increase - get_current()?
Date: 24 Jul 2003 12:28:46 +0100	[thread overview]
Message-ID: <1059046125.7993.11.camel@dhcp22.swansea.linux.org.uk> (raw)
In-Reply-To: <20030724050655.GA11947@beast>

On Iau, 2003-07-24 at 06:06, David McCullough wrote:
> Back when I first did the 2.4 uClinux port,  the m68k MMU code was
> dedicating a register (a2) for current.  I thought that was a bad idea
> given how often you run out of registers on the 68k,  and made it a

On some platforms a global register current was a win, I can't speak for
m68k - current is used a lot.

> On the 2.5/2.6 front,  I think the change comes from the 8K (2 page) task
> structure and everyone just masking the kernel stack pointer to get the
> task pointer.  Gerg would know for sure,  he did the 2.5 work in this area.
> We should be easily able to switch back to the current_task pointer with a
> few small mods to entry.S.

A lot of platforms went this way because "current" is hard to do right
on an SMP box. Its effectively per CPU dependant, and that means you
either set up the MMU to do per CPU pages (via segments or tables) which
is a pita, or you do the stack trick. For uniprocessor a global still
works perfectly well.

> A general comment on the use of inline throughout the kernel.  Although
> they may show gains on x86 platforms,  they often perform worse on 
> embedded processors with limited cache,  as well as adding size.  I

Code size for critical paths is getting more and more performance critical
on x86 as well as on the embedded CPU systems. 3Ghz superscalar processors
lose a lot of clocks to a memory stall.


  reply	other threads:[~2003-07-24 11:22 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-23 18:46 Kernel 2.6 size increase Bernardo Innocenti
2003-07-23 19:14 ` Richard B. Johnson
2003-07-23 20:07   ` David S. Miller
2003-07-23 21:47     ` Randy.Dunlap
2003-07-23 19:32 ` [uClinux-dev] " Christoph Hellwig
2003-07-23 20:11   ` David S. Miller
2003-07-23 20:15     ` Christoph Hellwig
2003-07-23 20:22       ` David S. Miller
2003-07-23 20:27         ` Christoph Hellwig
2003-07-23 22:35           ` [uClinux-dev] Kernel 2.6 size increase - get_current()? Bernardo Innocenti
2003-07-23 22:37             ` Alan Cox
2003-07-23 23:00               ` Bernardo Innocenti
2003-07-24  5:06                 ` David McCullough
2003-07-24 11:28                   ` Alan Cox [this message]
2003-07-24 12:04                     ` David McCullough
2003-07-24 14:48                       ` Alan Cox
2003-07-25 18:25                       ` bill davidsen
2003-07-24 15:30                     ` Hollis Blanchard
2003-07-24 19:37                       ` Alan Cox
2003-07-24 19:51                         ` Hollis Blanchard
2003-07-24 21:20                           ` J.A. Magallon
2003-07-25  4:22                             ` Otto Solares
2003-07-25 14:38                               ` Hollis Blanchard
2003-07-28  3:19                                 ` Miles Bader
2003-07-28  8:14                                   ` Ihar "Philips" Filipau
2003-07-28  8:58                                     ` Miles Bader
2003-07-28  9:03                                       ` Ihar "Philips" Filipau
2003-07-23 21:57   ` [uClinux-dev] Kernel 2.6 size increase Bernardo Innocenti
2003-07-23 22:07     ` Bernardo Innocenti
2003-07-23 22:27       ` Willy Tarreau
2003-07-23 22:34         ` Alan Cox
2003-07-24 20:27         ` Bernardo Innocenti
2003-07-25 15:46           ` Christoph Hellwig
2003-07-25 23:55             ` [PATCH] Make I/O schedulers optional (Was: Re: Kernel 2.6 size increase) Bernardo Innocenti
2003-07-26  8:17               ` Andrew Morton
2003-07-26 12:40                 ` Bernardo Innocenti
2003-07-26 14:07                   ` Jens Axboe
2003-07-26 23:42                     ` Bernardo Innocenti
2003-07-26 23:41                       ` Jens Axboe
2003-07-28 17:13             ` [uClinux-dev] Kernel 2.6 size increase Nicolas Pitre
2003-07-28 23:02               ` Bernardo Innocenti
2003-07-29  2:36                 ` Miles Bader
2003-08-08 13:25                 ` [uClinux-dev] " David Woodhouse
2003-08-08 14:37                   ` Bernardo Innocenti
2003-08-08 14:43                     ` David Woodhouse
2003-07-25 18:16           ` bill davidsen
2003-07-29 22:29           ` Tom Rini
2003-07-29 22:48             ` Alan Cox
2003-07-29 23:06               ` Tom Rini
2003-07-30  2:07                 ` Miles Bader
2003-07-30 15:33                   ` Tom Rini
2003-07-31  1:49                     ` Miles Bader
2003-07-31  4:17                       ` Tom Rini
2003-07-31  5:03                         ` Miles Bader
2003-07-31 15:24                           ` Tom Rini
2003-07-30  2:49             ` [uClinux-dev] " Bernardo Innocenti
2003-07-30 15:35               ` Tom Rini
2003-07-30 16:45                 ` [uClinux-dev] Kernel 2.6 size increase (PATCH) Bernardo Innocenti
     [not found] <cwQJ.3BO.29@gated-at.bofh.it>
     [not found] ` <cypH.5dM.35@gated-at.bofh.it>
     [not found]   ` <cyza.5lN.13@gated-at.bofh.it>
     [not found]     ` <cArg.74D.11@gated-at.bofh.it>
2003-07-24  8:13       ` [uClinux-dev] Kernel 2.6 size increase - get_current()? Ihar "Philips" Filipau
2003-07-25  7:25         ` Denis Vlasenko
2003-07-25 18:36         ` bill davidsen
2003-07-24  8:27 Ihar "Philips" Filipau
2003-07-24 11:50 ` David McCullough
     [not found] <d2nx.4QV.15@gated-at.bofh.it>
     [not found] ` <dbTZ.5Z5.19@gated-at.bofh.it>
2003-07-25 15:37   ` Ihar "Philips" Filipau

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