From: "H. Peter Anvin" <hpa@zytor.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>,
Asit K Mallick <asit.k.mallick@intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Avi Kivity <avi@redhat.com>,
Arjan van de Ven <arjan@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/9] x86/kernel/cpu/intel.c: Initialize Enhanced REP MOVSB/STOSBenhanced
Date: Tue, 17 May 2011 20:47:23 -0700 [thread overview]
Message-ID: <4DD3414B.2020602@zytor.com> (raw)
In-Reply-To: <ca1b13fa72e83adbc23b56e0cb28df7a.squirrel@www.firstfloor.org>
On 05/17/2011 07:46 PM, Andi Kleen wrote:
>> From: Fenghua Yu <fenghua.yu@intel.com>
>>
>> If kernel intends to use enhanced REP MOVSB/STOSB, it must ensure
>> IA32_MISC_ENABLE.Fast_String_Enable (bit 0) is set and CPUID.(EAX=07H,
>> ECX=0H):
>> EBX[bit 9] also reports 1.
>
> I suspect the check at this place is not too useful because it will
> only work for the BSP. For all others it's too late -- the patching
> has already happened.
>
> So either this is a problem and then it should be checked on all CPUs.
> Or maybe not at all.
>
> The problem is that the alternative patching currently relies on being
> run early with no other CPUs. It has no race protections, support
> for cross modification etc.
>
> While it would be possible to fix that it would be quite complicated
> I bet.
>
> So I think it's better to just remove it unless it's a real problem
> in the field.
>
The reason for having it is that if the BIOS has a chicken switch that
disables FAST_STRING (and it's the BIOS' responsibility to do it on all
CPUs) then this will make the kernel honor this.
-hpa
next prev parent reply other threads:[~2011-05-18 3:47 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-17 22:29 [PATCH 0/9] Optimize string operations by enhanced REP MOVSB/STOSB Fenghua Yu
2011-05-17 22:29 ` [PATCH 1/9] x86, cpu: Enable enhanced REP MOVSB/STOSB feature Fenghua Yu
2011-05-17 23:13 ` [tip:x86/cpufeature] x86, cpufeature: Add CPU feature bit for enhanced REP MOVSB/STOSB tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 2/9] x86/kernel/cpu/intel.c: Initialize Enhanced REP MOVSB/STOSBenhanced Fenghua Yu
2011-05-18 2:46 ` Andi Kleen
2011-05-18 3:47 ` H. Peter Anvin [this message]
2011-05-18 20:40 ` [tip:perf/core] x86, mem, intel: Initialize Enhanced REP MOVSB/STOSB tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 3/9] x86/kernel/alternative.c: Add comment for applying alternatives order Fenghua Yu
2011-05-18 20:40 ` [tip:perf/core] x86, alternative, doc: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 4/9] x86, alternative-asm.h: Add altinstruction_entry macro Fenghua Yu
2011-05-18 20:41 ` [tip:perf/core] x86, alternative: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 5/9] x86/lib/clear_page_64.S: Support clear_page() with enhanced REP MOVSB/STOSB Fenghua Yu
2011-05-18 20:41 ` [tip:perf/core] x86, mem: clear_page_64.S: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 6/9] x86/lib/copy_user_64.S: Support copy_to_user/copy_from_user by " Fenghua Yu
2011-05-18 20:42 ` [tip:perf/core] x86, mem: copy_user_64.S: Support copy_to/from_user " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 7/9] x86/lib/memcpy_64.S: Optimize memcpy " Fenghua Yu
2011-05-18 6:35 ` Ingo Molnar
2011-05-18 19:04 ` Yu, Fenghua
2011-05-18 20:42 ` [tip:perf/core] x86, mem: memcpy_64.S: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 8/9] x86/lib/memmove_64.S: Optimize memmove " Fenghua Yu
2011-05-18 20:43 ` [tip:perf/core] x86, mem: memmove_64.S: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 9/9] x86/lib/memset_64.S: Optimize memset " Fenghua Yu
2011-05-18 2:57 ` Andi Kleen
2011-05-18 3:09 ` Yu, Fenghua
2011-05-18 4:05 ` Andi Kleen
2011-05-18 18:33 ` Yu, Fenghua
2011-05-18 18:39 ` Andi Kleen
2011-05-18 18:47 ` Ingo Molnar
2011-05-18 18:49 ` Yu, Fenghua
2011-05-18 20:43 ` [tip:perf/core] x86, mem: memset_64.S: " tip-bot for Fenghua Yu
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