CAM disk I/O starvation

[Adrian Chadd]

On 11 April 2012 10:21, Gary Jennejohn <gljennjohn at googlemail.com> wrote:

> Just for the archive my bad disk performance seems to have been fixed in
> HEAD by svn commit r234074.  Seems that all interrupts were being handled
> by a single CPU/core (I have 6), which resulted in abysmal interrupt
> handling when mutltiple disks were busy.
>
> Since this commit my disk preformance is back to normal and long lags
> are a thing of the past.

Hi,

This is kind of worrying. You only have a few disks, a single core
SHOULD be able to handle all the interrupts for those disks whilst
leaving plenty of cycles to spare to drive the rest of your system.
And you have 5 other cores.

Would you be willing to help out diagnose exactly why that particular
behaviour is causing you so much trouble? It almost sounds like
something in the IO path is blocking for far too long, not allowing
the rest of the system to move forward. That's very worrying for an
interrupt handler. :)



Adrian