RE: [PATCH] x86: Add clflush before monitor for Intel 7400 series

From: Pallipadi, Venkatesh
Date: Fri Oct 17 2008 - 16:05:28 EST

>-----Original Message-----
>From: H. Peter Anvin [mailto:hpa@xxxxxxxxx]
>Sent: Tuesday, October 07, 2008 4:03 PM
>To: Pallipadi, Venkatesh
>Cc: Ingo Molnar; Thomas Gleixner; linux-kernel
>Subject: Re: [PATCH] x86: Add clflush before monitor for Intel
>7400 series
>Venki Pallipadi wrote:
>> Yes. Other alternative is to disable mwaits altogether on
>these CPUs. I can
>> send a patch to do that. But, the patch will be somewhat
>more complicated
>> as kernel advertises the MWAIT capability to firmware with a
>ACPI _PDC method
>> and BIOS has to then give IO port based C2 for us to use in
>such case.
>> Avoiding mwait just for C1 is easy though.
>It would be my weak preference, although I'm willing to be convinced
>that mwait is worth the power savings even with the workaround.
> -hpa


Do you still have reservations about this being expensive.
Note that this is only done when a CPU is about to go idle and
The cost of clflush itself will be minimal compared to idle
entry + idle exit latency.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at