Re: [PATCH] O13int for interactivity

[Nick Piggin]

Gene Heskett wrote:

> On Tuesday 12 August 2003 22:08, jw schultz wrote:
>
> > On Tue, Aug 12, 2003 at 09:58:04PM +1000, Nick Piggin wrote:
> >
> > > I have been hearing of people complaining the scheduler is worse
> > > than 2.4 so its not entirely obvious to me. But yeah lots of it is
> > > trial and error, so I'm not saying Con is wasting his time.
> > I've been watching Con and Ingo's efforts with the process
> > scheduler and i haven't seen people complaining that the
> > process scheduler is worse.  They have complained that
> > interactive processes seem to have more latency.  Con has
> > rightly questioned whether that might be because the process
> > scheduler has less control over CPU time allocation than in
> > 2.4.  Remember that the process scheduler only manages the
> > CPU time not spent in I/O and other overhead.
> >
> > If there is something in BIO chewing cycles it will wreak
> > havoc with latency no matter what you do about process
> > scheduling.  The work on BIO to improve bandwidth and reduce
> > latency was Herculean but the growing performance gap
> > between CPU and I/O is a formidable challenge.
>
> In thinking about this from the aspect of what I do here, this makes 
> quite a bit of sense.  In running 2.6.0-test3, with anticipatory 
> scheduler, it appears the i/o intensive tasks are being pushed back 
> in favor of interactivity, perhaps a bit too aggressively.  An amanda 
> estimate phase, which turns tar loose on the drives, had to be 
> advanced to a -10 niceness for the whole tree of processes amanda 
> spawns before it began to impact the setiathome use as shown by the 
> nice display in gkrellm.  Normally there is a period for maybe 20 
> minutes before the tape drive fires up where the machine is virtually 
> unusable due to gzip hogging things, like the cpu, during which time 
> seti could just as easily be swapped out.  It remained at around 60%!
>
> It did not hog/lag near as badly as usual, and the amanda run was over 
> an hour longer than it would have been in 2.4.22-rc2.
>
> It is my opinion that all this should have been at setiathomes 
> expense, which is also rather cpu intensive, but it didn't seem to be 
> without lots of forceing.  This is what the original concept of 
> niceness was all about.  Or at least that was my impression.  From 
> what it feels like here, it seems the i/o stuff is whats being 
> choked, and choked pretty badly when using the anticipatory 
> scheduler.
>
> I've read rumors that a boottime option can switch it to somethng 
> else, so what do I do to switch it from the anticipatory scheduler to 
> whatever the alternate is?, so that I can get a feel for the other 
> methods and results.

Boot with "elevator=deadline" to use the more conventional elevator.

It would be good if you could get some numbers 2.4 vs 2.6, with and
without seti running. Sounds like a long cycle though so you probably
can't be bothered!


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