Yet another INDEX builder.

[Kris Kennaway]

On Sat, Sep 30, 2006 at 03:49:51PM +0200, Michel Talon wrote:
> Kris Kennaway  said:
> 
> > FYI, I'm not sure if the python version is parallelizable, but you do
> > get a small benefit from using parallelized 'make index' builds (via
> > INDEX_JOBS) on a typical SMP machine.
> 
> My script runs parallel makes, of the order of ten simultaneous makes.

OK, FYI I see a performance drop if you use too much parallelism (10
is "far too much" on a typical system; ~3 is probably optimal for a
HTT machine).

> You can see them, running top at the same time, but of course they are very
> transient, since usually one make lasts of the order of 0.1 s on my machine.
> Anyways, still on my machine i have gained of the order of 20% wall clock time
> by doing that. And it is only an hyperthreaded P4 (running in SMP mode). This
> is why i was curious to know the effect of this idea on a machine with real
> SMP and perhaps disks supporting tagged queuing, which should allow better
> throughput for these simultaneous makes. I had, perhaps naively, assumed that
> with a good machine one can divide time by 2.

The only situation where you might reasonably expect to see something
approaching a factor of 2 speed improvement is if your ports tree is
on a striped or mirrored device on separate controllers, so 2 reads
can be completely decoupled from each other in hardware.  I've not
tried this though.

Kris
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