Messages in this thread | | | Subject | Re: Negative "ios_in_flight" in the 2.4 kernel | From | "M. Edward Borasky" <> | Date | Thu, 23 Dec 2004 07:30:04 -0800 |
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On Thu, 2004-12-23 at 09:08 +0100, Jens Axboe wrote: > > We could eliminate that possibility if you ran your tests with a single > > non-partitioned disk, but thats just a guess. > > It would be nice to know if this was a vanilla kernel or patched in some > way. The only recent bug in this area I remember was a bad merge in the > SUSE tree with the io_request_lock scaling patch.
I have seen this with Red Hat 2.4.18 (from RH 8.0) kernels, Gentoo 2.4.25 and 2.4.26 kernels, on both single-disk and two-disk systems. Now that I think of it, I've seen this on both single-processor and multi-processor systems and with both SCSI and IDE drives. I have also seen these systems run for quite a while without ios_in_flight going negative. And I've never seen ios_in_flight lower than -1 or higher than 0 on an idle system. So my conclusion is that an extra downcount is fairly rare.
I saw a very similar bug listed in the LKML about a year ago. For example, see
http://search.luky.org/linux-kernel.2004/msg00025.html
and
http://search.luky.org/linux-kernel.2004/msg03278.html
I think I'll try rebooting the two-disk box (which is easier to get one truly idle disk on) and running bonnie++ periodically to see if I can get steady-state ios_in_flight values other than -1 and 0 on an idle system (between bonnie++ runs). I can set up "oprofile" on the Gentoo boxes if that will help.
One other note: all of these systems when "idle" have a small amount of write activity going on. The Red Hat boxes are using ext3 filesystems and the Gentoo systems are using reiserfs. Is constant low-level writing to be expected with journaling?
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