kern.hz?

[elekktretterr]

Apparently a lot of people using FreeBSD use this to get semi-decent IO
performance in vmware. Do we have an equivalent for this feature?

Petr

[Thomas E. Spanjaard]

elekktretterr@... wrote:
> Apparently a lot of people using FreeBSD use this to get semi-decent IO
> performance in vmware. Do we have an equivalent for this feature?

Set HZ in your kernel config.

Cheers,
--
        Thomas E. Spanjaard
        tgen@...
        tgen@...

[Justin C. Sherrill]

On Fri, October 2, 2009 10:45 pm, elekktretterr@... wrote:
> Apparently a lot of people using FreeBSD use this to get semi-decent IO
> performance in vmware. Do we have an equivalent for this feature?

I recall from some previous discussion that this shouldn't have as
significant of an effect for DragonFly because of differences in the setup
between FreeBSD and DragonFly.  That's theoretical, though, so if you
modify those values, try to find some way of benchmarking before-and-after
(and report results back, please) so the difference, if any, is clear.

[Emil Mikulic-2]

On Sat, Oct 03, 2009 at 12:45:56PM +1000, elekktretterr@... wrote:
> Apparently a lot of people using FreeBSD use this to get semi-decent IO
> performance in vmware. Do we have an equivalent for this feature?

IO performance?

I tune it down (from FreeBSD's default of 1000) in order to reduce the
amount of CPU being used by the various timer interrupts when VMs are
[otherwise] idle.

IIRC DragonFlyBSD has HZ=100 by default and at some point FreeBSD
started detecting that it's being virtualized and tuning HZ down
without the user having to do it in /boot/loader.conf

[Matthew Dillon]

    DragonFly doesn't use kern.hz for much beyond the callout timers and
    tsleep.  It uses independant systimers for scheduling and network
    polling.  FreeBSD upped their hz default primarily for their scheduler
    and network polling insofar as I remember.

    This is why DragonFly's hz was left at 100, and changing hz in DragonFly
    will not have much of an effect.

    Our scheduler clock is currently hardwired via ESTCPUFREQ in sys/proc.h
    We could make it programmable via sysctl... changing the frequency is
    really easy since it uses a systimer.  That would be a fun project for
    someone if they wanted to do it.  Calculations based on ESTCPUFREQ would
    have to be adjusted to be based on a variable instead.  ESTCPUFREQ
    is 50Hz at the moment.

    The networking polling frequency is set with a sysctl and only used
    if one or more interfaces has polling turned on.

                                        -Matt
                                        Matthew Dillon
                                        <dillon@...>