Re: 2.6.8-rc1-np1

[Martin Schlemmer]

On Sat, 2004-07-17 at 11:25, Nick Piggin wrote:
> 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.
> 

Feels fine here on 3GHz P4 (HT system on i875 with dual channel
memory, striped raid ST38013AS HDD's).  xmms haven't skipped yet
(X reniced to -10) and desktop switching is quick.  First time
typing might be a bit sluggish in gnome-terminal, but second/third
char is fine, and vim seems to load fast enough.  All this is
with a 'make -j24' for kernel (yeah, not really that realistic,
but thought I should give it a go) and make -j4 for xorg-x11 going.
A few load values is:

load average: 26.72, 15.99, 7.35
load average: 27.93, 19.48, 9.52
load average: 28.02, 19.64, 9.63
load average: 26.01, 19.36, 9.59


base_timeslice is 256 btw ...

> > 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.
> > 
> 

Cannot say I can really feel this test.  That with 'make -j4' for
X have load:

load average: 2.74, 4.45, 5.98

where the last is still high from the make -j24.

> 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.
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-- 
Martin Schlemmer

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