Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt

Martin J. Bligh
2005-07-12T04:30:35Z

--Lee Revell <rlrevell@joe-job.com> wrote (on Tuesday, July 12, 2005 00:13:21 -0400):

> On Mon, 2005-07-11 at 21:07 -0700, Martin J. Bligh wrote:
>>
>> --Lee Revell <rlrevell@joe-job.com> wrote (on Monday, July 11, 2005 20:30:59 -0400):
>>
>> > On Mon, 2005-07-11 at 14:39 -0600, Chris Friesen wrote:
>> >> Lee Revell wrote:
>> >>
>> >> > Tickless + sub HZ timers is a win for everyone, the multimedia people
>> >> > get better latency, and the laptop people get to run longer.
>> >>
>> >> IIRC it's not a win for many systems. Throughput goes down due to timer
>> >> manipulation overhead.
>> >
>> > Makes sense. Anyway, this whole thread has been pretty hand wavey, I
>> > propose that until we see some numbers from the HZ=250 advocates, we
>> > leave the default alone.
>>
>> Odd. Since I showed you some numbers already ... and nobody from the latency
>> side of the argument has come up with any?
>
> Sorry, I have not seen any. Got a link?

Look back in the thread. It made kernel compiles about 5% faster on a
fairly large box. I think the SGI people did it originally because it
caused them even larger problems.

I'm not saying their aren't arguments on both sides ... there are. I just
agree with you there's a lot of hand-waving going on ... but probably not
agreeing as to who it's coming from ;-)

Some sort of comprimise has to be struck for now, until we get sub-HZ
timers. I'd prefer 100, personally (I had that set as default in my tree
for a long time). Some people would prefer 1000 or even more, maybe.
250/300 seems like a reasonable comprimise to me. Exactly what problems
*does* it cause (in visible effect, not "timers are less granular").
Jittery audio/video? How much worse is it?

M.