From: "Andi Kleen" <andi@firstfloor.org>
To: "Fenghua Yu" <fenghua.yu@intel.com>
Cc: "Ingo Molnar" <mingo@elte.hu>,
"Thomas Gleixner" <tglx@linutronix.de>,
"H Peter Anvin" <hpa@zytor.com>,
"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>,
"Andi Kleen" <andi@firstfloor.org>,
"linux-kernel" <linux-kernel@vger.kernel.org>,
"Fenghua Yu" <fenghua.yu@intel.com>
Subject: Re: [PATCH 2/9] x86/kernel/cpu/intel.c: Initialize Enhanced REP MOVSB/STOSBenhanced
Date: Wed, 18 May 2011 04:46:43 +0200 [thread overview]
Message-ID: <ca1b13fa72e83adbc23b56e0cb28df7a.squirrel@www.firstfloor.org> (raw)
In-Reply-To: <1305671358-14478-3-git-send-email-fenghua.yu@intel.com>
> 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.
-Andi
next prev parent reply other threads:[~2011-05-18 2:46 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 [this message]
2011-05-18 3:47 ` H. Peter Anvin
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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