----- Original Message ----- From: "Andreas Dilger" <adilger@clusterfs.com> To: "Andreas Jung" <andreas@zope.com> Cc: <ext3-users@redhat.com> Sent: Friday, May 24, 2002 14:11 Subject: Re: High load on Squid server after change from reiserfs to ext3 > On May 24, 2002 13:40 -0400, Andreas Jung wrote: > > From: "Andreas Dilger" <adilger@clusterfs.com> > > > One simple question - does the increase in the load value actually > > > affect squid performance? You say there is no increase in CPU > > > utilization. That may be good or it may be bad, depending if the "idle" > > > CPU is actually waiting on I/O to complete. > > > > > > What does the output of vmstat on both systems show? Please send two > > > traces, one during low load and one during high load. > > > > Our big brother diagrams show that the CPU utilization remains *low* all > > the time. I have been running vmstat on both machines when one of the > > machine had a spike. But both machines showed more ore less identical > > vmstat output: CPU was about 85% idle, no swapping, not much interrupts > > and context switches. > > In general, vmstat showed a perfect behaviour except that the load average > > went up on one box. > > Then it is nothing to worry about. The "load average" does not indicate > anything other than the number of processes runnable or waiting for > disk I/O. It is likely that when you are doing a large journal flush > the kjournald process is waiting for the disk I/O to complete, so it is > counted 1 towards the load average. This in itself does not affect the > performance of the system. > That's right but we see these spikes sometimes over a period of 3-4 hours. And there is only a moderate disk IO during that time of about 2GB/hour since the squids have a very high overall highrate of 96% (50% memory hits). Andreas
