RE: [patch] prefer TSC over PM Timer

From: dean gaudet (dean-list-linux-kernel_at_arctic.org)
Date: 11/17/04

  • Next message: David S. Miller: "loops in get_user_pages() for VM_IO" 
    Date:	Tue, 16 Nov 2004 17:50:42 -0800 (PST)
To: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>

    On Tue, 16 Nov 2004, Pallipadi, Venkatesh wrote:

    > I think trying to remove repeated inl()'s in read_pmtmr is a better
    > fix for this issue. As John mentioned in other thread, we should do
    > repeated reads only when something looks broken. Not always.

    that would be a nice improvement... then timer_pm will only be 3x as slow
    as timer_tsc instead of 10x slower :) it's still a lot of unnecessary
    overhead for many systems, and unfortunately this is a real performance
    problem (albeit exaggerated by code which is overzealous in its use of
    gettimeofday()).

    on a tangent... has the local apic timer ever been considered? it's fixed
    rate, and my measurements show it in the same performance ballpark as TSC.

    i know that all p3, p-m, p4, k8 and efficeon have local APIC, but i'm not
    sure if k7 (other than k7 smp parts of course) have local apics... so i'm
    not sure how widespread it is compared to pm-timer.

    wouldn't local apic timer be a lot better for NUMA too?

    hey wait, what exactly is the problem with TSC on NUMA? don't you just
    need some per-cpu data (epoch and calibration) to make it work?

    -dean
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