linux-kernel - Re: [RFC 2/2] x86_64: expand kernel stack to 16K

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Date:	Wed, 28 May 2014 18:11:25 +0200
From:	Richard Weinberger <richard@....at>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Minchan Kim <minchan@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>, mst@...hat.com,
	Dave Hansen <dave.hansen@...el.com>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K

Am 28.05.2014 18:08, schrieb Steven Rostedt:
> On Wed, 28 May 2014 17:43:50 +0200
> Richard Weinberger <richard.weinberger@...il.com> wrote:
> 
> 
>>> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
>>> index 8de6d9cf3b95..678205195ae1 100644
>>> --- a/arch/x86/include/asm/page_64_types.h
>>> +++ b/arch/x86/include/asm/page_64_types.h
>>> @@ -1,7 +1,7 @@
>>>  #ifndef _ASM_X86_PAGE_64_DEFS_H
>>>  #define _ASM_X86_PAGE_64_DEFS_H
>>>
>>> -#define THREAD_SIZE_ORDER      1
>>> +#define THREAD_SIZE_ORDER      2
>>>  #define THREAD_SIZE  (PAGE_SIZE << THREAD_SIZE_ORDER)
>>>  #define CURRENT_MASK (~(THREAD_SIZE - 1))
>>
>> Do you have any numbers of the performance impact of this?
>>
> 
> What performance impact are you looking for? Now if the system is short
> on memory, it would probably cause issues in creating tasks. But other
> than that, I'm not sure what you are looking for.

Allocating more continuous memory for every thread is not cheap.
I'd assume that such a change will cause more pressure on the allocator.

Thanks,
//richard
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