On Wed, Aug 10, 2011 at 11:05 AM, Yu, Fenghua [off-list ref] wrote:

quoted

-----Original Message-----
From: amluto@gmail.com [mailto:amluto@gmail.com] On Behalf Of Andrew
Lutomirski
Sent: Wednesday, August 10, 2011 7:50 AM
To: Yu, Fenghua
Cc: x86@kernel.org; linux-kernel@vger.kernel.org; Matthew Garrett; Len
Brown; linux-acpi@vger.kernel.org; Ingo Molnar; Anvin, H Peter
Subject: Re: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
hasn't already

On Tue, Aug 9, 2011 at 11:40 AM, Yu, Fenghua [off-list ref]
wrote:

quoted

quoted

-----Original Message-----
From: Andy Lutomirski [mailto:luto@MIT.EDU]
Sent: Tuesday, August 09, 2011 5:41 AM
To: x86@kernel.org; linux-kernel@vger.kernel.org
Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
acpi@vger.kernel.org; Ingo Molnar; Andy Lutomirski
Subject: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
hasn't already

Intel SDM volume 3A, 8.4.2 says:

  Software can disable fast-string operation by clearing the
  fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR.
  However, Intel recomments that system software always enable
  fast-string operation.

The Intel DQ67SW board (with latest BIOS) disables fast string
operations if TXT is enabled.  A Lenovo X220 disables it regardless
of TXT setting.  I doubt I'm the only person with a dumb BIOS like
this.

Signed-off-by: Andy Lutomirski <redacted>
---
 arch/x86/kernel/cpu/intel.c |   28 +++++++++++++++++++++++-----
 1 files changed, 23 insertions(+), 5 deletions(-)

Signed-off-by: Fenghua Yu <redacted>

Please don't apply.  This patch breaks !CONFIG_SMP.  I'll send a fixed
patch later on.

+                               printk_once(KERN_INFO FW_WARN "CPU #%d: IA32_MISC_ENABLE.FAST_STRING_ENABLE was not set",
There is no need to print CPU id. Then there is no SMP issue.

True, and with the printk_once change it's pointless.  I was printing
it because of the other patch: my BIOS enables monitor/mwait on some,
but not all, CPUs.  (Working around that is a little less optional.
My systems gets lucky because it's off on the boot CPU so the idle
loop doesn't call mwait.  If it were the other way around, the kernel
would presumably oops quickly.)

--Andy
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