Paul Davis wrote:
> this is not strictly true. the IDE drivers (and devices) are the worst
> offenders, but they are far the only place in the mainstream kernel
> where the kernel could block a runnable task for a (very) long time.
Besides the kernel preemption patch and lowlatency patches, does the
hdparm command "-u1" help this?
>From the hdparm man page:
-u Get/set interrupt-unmask flag for the drive. A
setting of 1 permits the driver to unmask other
interrupts during processing of a disk interrupt,
which greatly improves Linux's responsiveness and
eliminates "serial port overrun" errors. Use this
feature with caution: some drive/controller combi�
nations do not tolerate the increased I/O latencies
possible when this feature is enabled, resulting in
massive filesystem corruption. In particular,
CMD-640B and RZ1000 (E)IDE interfaces can be unre�
liable (due to a hardware flaw) when this option is
used with kernel versions earlier than 2.0.13.
Disabling the IDE prefetch feature of these inter�
faces (usually a BIOS/CMOS setting) provides a safe
fix for the problem for use with earlier kernels.\
As far as I know, -u1 is safe with all modern hard drive
controllers, and it sounds like it could help latencies related
to IDE quite a bit.
Torrey
