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From: Rusty Russell <rusty@rustcorp.com.au>
To: Ingo Molnar <mingo@elte.hu>
Cc: lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Zachary Amsden <zach@vmware.com>,
	Jeremy Fitzhardinge <jeremy@xensource.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andi Kleen <ak@suse.de>
Subject: Re: [PATCH 6/8] Allow per-cpu variables to be page-aligned
Date: Wed, 07 Mar 2007 11:16:48 +1100	[thread overview]
Message-ID: <1173226608.4644.59.camel@localhost.localdomain> (raw)
In-Reply-To: <20070306131522.GC9031@elte.hu>

On Tue, 2007-03-06 at 14:15 +0100, Ingo Molnar wrote:
> * Rusty Russell <rusty@rustcorp.com.au> wrote:
> 
> > Xen wants page-aligned GDT (and PDA must not cross a page-boundary, 
> > but that doesn't happen at the moment since it's so close to start of 
> > page).  Let's allow page-alignment in general for per-cpu data.
> > 
> > Because larger alignments can use more room, we increase the max 
> > per-cpu memory to 64k rather than 32k: it's getting a little tight.
> 
> i recently needed page-aligned per-cpu data too for KVM-paravirt. Btw., 
> what's the size increase of the native kernel?

To clarify for those reading fast, this patch doesn't increase at all,
since noone uses page-alignment.  For the next patch which aligns the
gdt, it's about +12k (21k -> 33k), but then we take away the pda in the
next patch and it drops back to +8k (the pda is in the same file as the
gdt, and on my system at least it ends up getting its own 4k alignment
too).

AFAICT, we could save the wasted partial page in three ways: by trying
to link it first, if it's only a case of one file, by having a special
page-aligned percpu data section, or by having a smarter linker.

Cheers,
Rusty.



  reply	other threads:[~2007-03-07  0:17 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-03-06 12:39 [PATCH 0/8] x86 boot, pda and gdt cleanups Rusty Russell
2007-03-06 12:53 ` [PATCH 1/8] Remove cpu_gdt_table: use boot_gdt_table until migration to per-cpu Rusty Russell
2007-03-06 12:54   ` [PATCH 2/8] Remove NR_CPUS from asm-generic/percpu.h Rusty Russell
2007-03-06 12:55     ` [PATCH 3/8] Use per-cpu variables for GDT, PDA Rusty Russell
2007-03-06 12:57       ` [PATCH 4/8] Cleanup setup_pda Rusty Russell
2007-03-06 12:58         ` [PATCH 5/8] Cleanup GDT access Rusty Russell
2007-03-06 13:00           ` [PATCH 6/8] Allow per-cpu variables to be page-aligned Rusty Russell
2007-03-06 13:01             ` [PATCH 7/8] Page-align the GDT Rusty Russell
2007-03-06 13:03               ` [PATCH 8/8] Convert PDA into the percpu section Rusty Russell
2007-03-06 13:10                 ` Ingo Molnar
2007-03-07  0:12                   ` Rusty Russell
2007-03-07  0:35                     ` Jeremy Fitzhardinge
2007-03-06 18:28                 ` Jeremy Fitzhardinge
2007-03-06 19:34                 ` Andi Kleen
2007-03-06 18:37                   ` Jeremy Fitzhardinge
2007-03-07  0:33                   ` Rusty Russell
2007-03-07 11:55                     ` Rusty Russell
2007-03-13 17:15                 ` Jeremy Fitzhardinge
2007-03-14  2:27                   ` Rusty Russell
2007-03-06 13:15             ` [PATCH 6/8] Allow per-cpu variables to be page-aligned Ingo Molnar
2007-03-07  0:16               ` Rusty Russell [this message]
2007-03-07  0:44                 ` H. Peter Anvin
2007-03-06 18:17             ` Jeremy Fitzhardinge
2007-03-07  0:29               ` Rusty Russell
2007-03-06 18:16           ` [PATCH 5/8] Cleanup GDT access Jeremy Fitzhardinge
2007-03-06 18:14       ` [PATCH 3/8] Use per-cpu variables for GDT, PDA Jeremy Fitzhardinge
2007-03-06 13:21     ` [PATCH 2/8] Remove NR_CPUS from asm-generic/percpu.h Ingo Molnar
2007-03-06 13:20   ` [PATCH 1/8] Remove cpu_gdt_table: use boot_gdt_table until migration to per-cpu Ingo Molnar
2007-03-06 13:26     ` Ingo Molnar
2007-03-07  0:22     ` Rusty Russell
2007-03-13 20:48 ` [PATCH 0/8] x86 boot, pda and gdt cleanups Jeremy Fitzhardinge
2007-03-14  2:25   ` Rusty Russell
2007-03-14  4:39     ` Jeremy Fitzhardinge
2007-03-14  6:54       ` Rusty Russell
2007-03-14 23:55   ` Rusty Russell
2007-03-15  1:57     ` Jeremy Fitzhardinge

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