6.2 SHOWSTOPPER - em completely unusable on 6.2

[Peter Jeremy]

On Wed, 2006-Sep-27 10:32:49 -0600, Scott Long wrote:
>My theory here is that something in the kernel, likely VM/VFS, is
>holding the Giant lock for an inordinate amount of time.

In the past (RELENG_5) I've had major problems with syncer delaying
interrupt threads for long periods (I've seen 8msec).  See
http://lists.freebsd.org/pipermail/freebsd-stable/2005-February/012346.html
I'm not sure if this is still a problem (but I am still having some
problems which may be caused by excessive interrupt and will be doing
some debugging as I get time).

>I have a few ideas on tracking down the root cause, but they are pretty
>pretty painful and slow.

In my case, I was fairly certain that the problem I was seeing was
excessive interrupt latency for my driver.  The approach I took was to
capture TSC, IRQ number and curproc address in lapic_handle_intr(),
atpic_handle_intr() and at the beginning of my interrupt handler into
a ring buffer.  I'd dump the ring buffer into a file using a userland
tool and then post-process the file looking for oddities.  In my case,
there was a _very_ high correlation between long latencies and syncer.
If anyone's interested in this approach, I can provide the relevant
code diffs.

>2. Add INTR_FAST shims to the usb and ichsmb drivers so that neither
>uses an ithread.

The problem I ran into with this approach was that my interrupt
handler needs to use psignal(9) - which requires PROC_LOCK() which
(AFAIK) isn't allowed in an INTR_FAST handler.

It would be useful if our interrupt subsystem allowed both INTR_FAST
and normal interrupt handlers to be defined.  If an INTR_FAST handler
is defined then it gets executed and defines whether its associated
interrupt thread handler needs to be triggered.  If there's no
INTR_FAST handler then the interrupt thread is always triggered.

-- 
Peter Jeremy
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20060927/dd3105c7/attachment.pgp