Re: i/o wait eating all of CPU on 2.6.1

[davidsen@tmr.com (bill davidsen)]

In article <20040125143042.GA20274@ihme.org>,
Jaakko Helminen  <haukkari@ihme.org> wrote:
| 
| I have two servers, both of which have more than 300 gigabytes of hard drive
| space and those files are made available to the network with samba, nfs and
| http and it worked fine with 2.6.0 but when I upgraded to 2.6.1 I noticed
| that everything was VERY slow, from a machine that is connected to the other
| server with a 100M link, 57kB/s tops. i/o wait eats up all of the cpu.
| On the other hand, Apache (and everything else) works very fast when I only
| send /dev/zero to a client, since that doesn't need disk operations.

Actually, io-wait is an indication that the CPU is idle with io
outstanding, and doesn't eat the machine any more than idle time. It is
an indication that the io is not keeping up, of course.

The fact that sending /dev/zero is fast sort of eliminates the reported
problems with NFS and setting the read/write size to 8k on the client.
Just for grins, hopefully you have followed the "NFS is slow" thread,
but I saw people having the issue with 2.6.0, so that's not likely to be
be involved.

I have some preliminary numbers which indicate 2.6.2-rc2 is faster at
some disk operations than 2.6.1, but since that's one benchmark on one
machine all I can say is that if you want to move forward, that kernel
is working well for me. Of course if there's nothing in 2.6.1 you
really want or need, falling back is a sure cure.

-- 
bill davidsen <davidsen@tmr.com>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.