Re: 2.6.8-rc1-np1

[Nick Piggin <nickpiggin@yahoo.com.au>]

Felipe Alfaro Solana wrote:
> On Sat, 2004-07-17 at 15:23 +1000, Nick Piggin wrote:
> 
> 
>>Scheduler behaviour is generally pretty good now so I've increased the
>>timeslice size to see how far I can push it. Some workloads really demand
>>small timeslices though, so I've added /proc/sys/kernel/base_timeslice.
>>If you have any problems with the default, please report it to me, and
>>check if lowering this value helps.
> 
> 
> On my 700Mhz Pentium III Mobile laptop, I feel that 256ms is too high
> for the system to keep interactive when a CPU hog is running. For

Yeah, it is probably a bit too large here too. A burst of activity
from X can cause xmms to skip slightly. Probably 128 or 64 would
be a decent default.

> example, running "while true; do a=2; done" makes the system pretty
> sluggish with the default timeslice. This is noticeable while dragging
> windows around (the movement is jerky and doesn't feel smooth).
> Decreasing the timeslie to 50ms, or even better, 25ms, makes the system
> behave much much better, although it will decrease throughput
> considerably, I guess.
> 

It usually isn't too bad for desktops, but is more important on
systems with more CPUs and bigger caches.

On this dual P3 with 256K L2 cache, a make -j8 vmlinux uses
162.16user 15.43system, ~150ctxsw/s with base_timeslice = 10000
163.88user 16.16system, ~300ctxsw/s with base_timeslice = 32
192.65user 17.27system, ~1300ctxsw/s with base_timeslice = 1

So you come to the point of diminishing returns very quickly, and
32 or even 16 or 8 are probably fine values for a desktop system
and worth the small cost for CPU intensive tasks.