Messages in this thread | | | From | "Pallipadi, Venkatesh" <> | Date | Fri, 17 Oct 2008 13:05:00 -0700 | Subject | RE: [PATCH] x86: Add clflush before monitor for Intel 7400 series |
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>-----Original Message----- >From: H. Peter Anvin [mailto:hpa@zytor.com] >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
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.
Thanks, Venki
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