Re: [PATCH] schedstat-2.6.0-test5-A1 measuring process scheduling latency

[Peter Chubb]

>>>>> "Rick" == Rick Lindsley <ricklind@xxxxxxxxxx> writes:


    
Rick> I'm not sure that it's any less or more intrusive, but it's at
Rick> least another way of doing the same thing.  So since you've
Rick> taken some measurements, what's the length of time you find your
Rick> process waits to hit the processor after getting the I/O it
Rick> needs?  What's the time it seems to wait when it skips (what's
Rick> the cutoff at which you hear a skip versus don't hear one?)


In short, time on the run queue is negligeable.  Time spend waiting
for disk I/O is extensive.  If you look at the graph, you'll see each
disk I/O takes 0.8 seconds, which is about the same as the skip.  This
is on ReiserFS 2.6, laptop (4000RPM) disk, but attached to mains
power.

There's a massive difference between the behaviour with hdparm -u1 and
hdparm -u0 --- I don't see skips with -u1, and the time the disk light
is on is much reduced.  This puts my problem in the IDE layer
somewhere -- which means it may not be the same problem others are
seeing.

--
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
You are lost in a maze of BitKeeper repositories,   all slightly different.
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