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    Subjectgettimeofday order of magnitude slower with pmtimer, which is default
    Hi everybody,

    For my open source nameserver (http://www.powerdns.com) I need to do quite a
    number of gettimeofday calls. I've pared it down to almost the bare minimum
    of 1 gettimeofday per packet sent and received. With these calls, I can make
    stats like http://ds9a.nl/tmp/rrd/ which my users need so they can verify
    the proper performance of the nameserver.

    Yesterday, together with Zwane, I discovered each gettimeofday call costs me
    4 usec on some boxes and almost nothing on others. We did a fruitless chase
    for vsyscall/sysenter happening but the problem turned out to be
    CONFIG_X86_PM_TIMER.

    This problem has been discussed before
    http://www.ussg.iu.edu/hypermail/linux/kernel/0411.1/2135.html

    Not only is the pm timer slow by design, it also needs to be read multiple
    times to work around a bug in certain hardware.

    What is new is that this option is now dependent on CONFIG_EMBEDDED. Unless
    you select this option, the PM Timer will always be used.

    Would a patch removing the link to EMBEDDED and adding a warning that while
    this timer is of high quality, it is slow, be welcome?

    Thanks.

    --
    http://www.PowerDNS.com Open source, database driven DNS Software
    http://netherlabs.nl Open and Closed source services
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