excessive use of gettimeofday(2) and other syscalls

[Rayson Ho]

There are some recent discussions on the freebsd-current list. The
infrastructure is there to provide a common shared page for processes
to mmap into the address space... but according to Kip's comment, libc
support is not there yet:

http://lists.freebsd.org/pipermail/freebsd-current/2011-June/025191.html

Also, the kernel needs to update the variable in that shared page on
each clock interrupt (depending on the resolution I believe), and I
think that needs to be added too.

IMO, the time returned by gettimeofday does not need to be high
precision. There are higher resolution time APIs on Linux and I
believe the application programmers know when to use the slower but
more accurate clock API. (At least in Grid Engine we only need a quick
way of getting the current time, and we don't care if it is precise to
the nanosecond range.)

See Linux security issue & solution: http://lwn.net/Articles/446528/
See also the Google SoC idea:
http://wiki.freebsd.org/IdeasPage#Timecounter_Performance_Improvements_.28GSoC.29

Rayson

=================================
Grid Engine / Open Grid Scheduler
http://gridscheduler.sourceforge.net


On Tue, Sep 6, 2011 at 8:49 PM, Manish Vachharajani
<manishv at lineratesystems.com> wrote:
> I believe that Linux uses a less precise clock that scales better
> across cores and is much faster than the precise clock FreeBSD uses
> even on one core.  I don't know POSIX and other standards well enough
> to know if this is an acceptable solution on FreeBSD.  However, there
> are less precise clocks on FreeBSD that are considerably faster (i.e.,
> the _FAST variants).  Someone with more expertise in these matters
> needs to comment on whether a change to using a _FAST clock is
> appropriate in libc.  If it is acceptable, I think that it is easier
> to just make time use the FAST clock instead of getting programmers to
> change their programs.
>
> On Tue, Sep 6, 2011 at 6:41 PM, Eitan Adler <lists at eitanadler.com> wrote:
>> On Tue, Sep 6, 2011 at 6:44 PM, Manish Vachharajani
>> <manishv at lineratesystems.com> wrote:
>>> Lots of libraries assume that time is fast because it
>>> is fast under Linux.
>>
>> Silly question, but why can't we make it fast too?
>>
>> --
>> Eitan Adler
>>
>
> Manish
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-- 
Rayson

==================================================
Open Grid Scheduler - The Official Open Source Grid Engine
http://gridscheduler.sourceforge.net/