"Steven M. Bellovin" <smb@cs.columbia.edu> writes:
> I recently upgraded my kernel to one from January 8 (and then to one
> from today).  Before that, I'd been running a mid-December -current.
>
> Interactive performance on my Thinkpad T42 has become completely
> unacceptable.  Something else -- I have no idea what -- occasionally
> grabs the CPU.  Moving the mouse shows jerky cursor motion, I get
> doubled input characters, etc.  ps and top show that the machine is
> mostly idle, though xosview sometimes shows brief spurts of 100% busy.
> It isn't swapping (it's got 2G of RAM), the interrupt load doesn't seem
> high (about 1.4-1.6K/sec, with HZ set to 1000), etc.  
>
> Is anyone else seeing this?  Anything I should do to tune it?  Might
> the new scheduler code be part of it?

I can explain exactly what is going on but not why.

This sort of thing was very routine for me before before BUFQ_READPRIO
(which was once called NEW_BUFQ_STRATEGY). Once I added that to my
kernel years ago, the problem went away. I suspect you have that in
your kernel.

As of Jan, something seems to have broken BUFQ_READPRIO -- unclear who
did it or why, but it is very clear to me that it got broken. The
old symptoms of lots of disk i/o locking out userland processes trying
to read something have returned.

Perry