* [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda
@ 2008-12-31 21:44 Ravikiran G Thirumalai
2008-12-31 22:18 ` Mike Travis
2009-01-02 16:09 ` Ingo Molnar
0 siblings, 2 replies; 5+ messages in thread
From: Ravikiran G Thirumalai @ 2008-12-31 21:44 UTC (permalink / raw)
To: Ingo Molnar; +Cc: linux-kernel, travis
The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
to remove static boot cpu pdas introduced a bug. _boot_cpu_pda is the
actual pda used by the boot cpu and is definitely not "__read_mostly" and
ended up polluting the read mostly section with writes. This bug caused
regression of about 8-10% on certain syscall intensive workloads.
Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Index: linux-2.6/arch/x86/kernel/head64.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/head64.c 2008-12-30 15:28:08.000000000 -0800
+++ linux-2.6/arch/x86/kernel/head64.c 2008-12-31 10:36:21.000000000 -0800
@@ -27,7 +27,7 @@
#include <asm/trampoline.h>
/* boot cpu pda */
-static struct x8664_pda _boot_cpu_pda __read_mostly;
+static struct x8664_pda _boot_cpu_pda;
#ifdef CONFIG_SMP
/*
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda
2008-12-31 21:44 [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda Ravikiran G Thirumalai
@ 2008-12-31 22:18 ` Mike Travis
2009-01-02 16:09 ` Ingo Molnar
1 sibling, 0 replies; 5+ messages in thread
From: Mike Travis @ 2008-12-31 22:18 UTC (permalink / raw)
To: Ravikiran G Thirumalai; +Cc: Ingo Molnar, linux-kernel
Ravikiran G Thirumalai wrote:
> The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
> to remove static boot cpu pdas introduced a bug. _boot_cpu_pda is the
> actual pda used by the boot cpu and is definitely not "__read_mostly" and
> ended up polluting the read mostly section with writes. This bug caused
> regression of about 8-10% on certain syscall intensive workloads.
>
> Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
>
> Index: linux-2.6/arch/x86/kernel/head64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/head64.c 2008-12-30 15:28:08.000000000 -0800
> +++ linux-2.6/arch/x86/kernel/head64.c 2008-12-31 10:36:21.000000000 -0800
> @@ -27,7 +27,7 @@
> #include <asm/trampoline.h>
>
> /* boot cpu pda */
> -static struct x8664_pda _boot_cpu_pda __read_mostly;
> +static struct x8664_pda _boot_cpu_pda;
>
> #ifdef CONFIG_SMP
> /*
Thanks for catching that!
Mike
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda
2008-12-31 21:44 [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda Ravikiran G Thirumalai
2008-12-31 22:18 ` Mike Travis
@ 2009-01-02 16:09 ` Ingo Molnar
2009-01-02 18:55 ` Ravikiran G Thirumalai
1 sibling, 1 reply; 5+ messages in thread
From: Ingo Molnar @ 2009-01-02 16:09 UTC (permalink / raw)
To: Ravikiran G Thirumalai; +Cc: linux-kernel, travis
* Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
> to remove static boot cpu pdas introduced a bug. _boot_cpu_pda is the
> actual pda used by the boot cpu and is definitely not "__read_mostly" and
> ended up polluting the read mostly section with writes. This bug caused
> regression of about 8-10% on certain syscall intensive workloads.
>
> Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
applied to tip/x86/urgent, with a Cc: stable tag. Thanks,
Ingo
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda
2009-01-02 16:09 ` Ingo Molnar
@ 2009-01-02 18:55 ` Ravikiran G Thirumalai
2009-01-02 19:20 ` Ingo Molnar
0 siblings, 1 reply; 5+ messages in thread
From: Ravikiran G Thirumalai @ 2009-01-02 18:55 UTC (permalink / raw)
To: Ingo Molnar; +Cc: linux-kernel, travis, stable, shai
[-- Attachment #1: Type: text/plain, Size: 788 bytes --]
On Fri, Jan 02, 2009 at 05:09:51PM +0100, Ingo Molnar wrote:
>
>* Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
>
>> The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
>> to remove static boot cpu pdas introduced a bug. _boot_cpu_pda is the
>> actual pda used by the boot cpu and is definitely not "__read_mostly" and
>> ended up polluting the read mostly section with writes. This bug caused
>> regression of about 8-10% on certain syscall intensive workloads.
>>
>> Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
>
>applied to tip/x86/urgent, with a Cc: stable tag. Thanks,
>
Thanks!
Stable maintainers, please consider this for 2.6.27 stable as well
(in addition to 28). (Attaching the tip/x86/urgent commit as reference to
the patch)
Thanks,
Kiran
[-- Attachment #2: fix_incorrect_readmostly --]
[-- Type: text/plain, Size: 1118 bytes --]
commit 26799a63110dcbe81291ea53178f6b4810d07424
Author: Ravikiran G Thirumalai <kiran@scalex86.org>
Date: Wed Dec 31 13:44:46 2008 -0800
x86: fix incorrect __read_mostly on _boot_cpu_pda
The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
to remove static boot cpu pdas introduced a performance bug.
_boot_cpu_pda is the actual pda used by the boot cpu and is definitely
not "__read_mostly" and ended up polluting the read mostly section with
writes. This bug caused regression of about 8-10% on certain syscall
intensive workloads.
Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Acked-by: Mike Travis <travis@sgi.com>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 388e05a..b9a4d8c 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -27,7 +27,7 @@
#include <asm/trampoline.h>
/* boot cpu pda */
-static struct x8664_pda _boot_cpu_pda __read_mostly;
+static struct x8664_pda _boot_cpu_pda;
#ifdef CONFIG_SMP
/*
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda
2009-01-02 18:55 ` Ravikiran G Thirumalai
@ 2009-01-02 19:20 ` Ingo Molnar
0 siblings, 0 replies; 5+ messages in thread
From: Ingo Molnar @ 2009-01-02 19:20 UTC (permalink / raw)
To: Ravikiran G Thirumalai; +Cc: linux-kernel, travis, stable, shai
* Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> On Fri, Jan 02, 2009 at 05:09:51PM +0100, Ingo Molnar wrote:
> >
> >* Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> >
> >> The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
> >> to remove static boot cpu pdas introduced a bug. _boot_cpu_pda is the
> >> actual pda used by the boot cpu and is definitely not "__read_mostly" and
> >> ended up polluting the read mostly section with writes. This bug caused
> >> regression of about 8-10% on certain syscall intensive workloads.
> >>
> >> Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
> >
> >applied to tip/x86/urgent, with a Cc: stable tag. Thanks,
> >
>
> Thanks!
>
> Stable maintainers, please consider this for 2.6.27 stable as well (in
> addition to 28). (Attaching the tip/x86/urgent commit as reference to
> the patch)
i have added a -stable tag to the commit - please only put it into -stable
once it hits Linus's tree. (in the next couple of days)
>
Ingo
^ permalink raw reply [flat|nested] 5+ messages in thread
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2008-12-31 21:44 [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda Ravikiran G Thirumalai
2008-12-31 22:18 ` Mike Travis
2009-01-02 16:09 ` Ingo Molnar
2009-01-02 18:55 ` Ravikiran G Thirumalai
2009-01-02 19:20 ` Ingo Molnar
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