Re: Serial Console and Slow SCSI Disk Access?

Jeff Gold
2006-06-19T15:14:19Z

Helge Hafting wrote:
> With nothing attached, any write to the serial device might go
> through a lengthy timeout because of flow control. [...] But I can't
> see why it'd make scsi disks slower. The scsi host adapter
> initialization writes some messages of course, but there should be no
> more console accesses during a hdparm test run.

This makes sense to me. When I attach a serial cable and use that to
login (I've got agetty running), hdparm produces no console messages
that I can see using minicom. Still, the disk throughput is around 1.5
MB/sec for some reason. When I disable the serial console in grub.conf
and reboot I get over 70 MB/sec again.

A combination of out-of-tree patches (mainly network related but also
one to disable PM_TIMERS) seem to eliminate the issue even with the
serial console enabled, at least for the moment. That means I no longer
have a problem, but the whole thing is mysterious to me.

Jeff