Re: Interrupt latency problems

On Sat, 2003-05-10 at 15:41, Soeren Schmidt wrote:
> It seems Paul Richards wrote:
> > I'm having real problems with current with heavy disk activity.
> > 
> > When working in X and updating ports which causes a lot of disk activity
> > I get *very* poor interactive responses. Keypresses can not appear for
> > seconds and mouse movement is very jerky and unresponsive.
> > 
> > I'm wondering if something is holding locks a long time in interrupt
> > handlers and causing mouse/keyboard interrupts to be lost?
> > 
> > Since this is caused by heavy disk activity then my first guess would be
> > the ATA driver.
> 
> Well, sortof, we have this lock called Giant, and we need all drivers
> to get out from under that. Now I have a plan to implement this in
> the ATA driver, but its rather complex to get it done right, and my
> spare time is limitted, meaning its not going to be done tomorrow...

Well, it doesn't look like it's specifically ATA since people with SCSI
are seeing it too. Sorry for pointing at ATA Soren, it's just definitely
disk related and this is an ATA box :-)

I'm not sure it's as simple as Giant though. We have a great big Giant
in 4.X and I don't see the same problem there. Something in -current is
not working right on SMP (I also don't have a single processor box to
hand to confirm it's just SMP either) that's making the system virtually
unuseable as a workstation.

Surely the remnants of Giant in a lot of the kernel should just degrade
the behaviour to being like the single big lock we had before, rather
than causing these big latencies that people are seeing? (of course the
locking mechanisms we now have are heavier than the simple kernel lock
we had before but even so, what I'm seeing is really severe).

Is everyone seeing this? If not then perhaps we can narrow down the
problem and look at getting things improved before 5-stable, because if
it stays like this it's not really what I'd consider useable.

> > Paul Richards <paul_at_freebsd-services.com>
> > FreeBSD Services Ltd
> 
> <soabbox>
> Now, if you are talking as freebsd-services as this implies, why dont
> you guys use some of the $$ you make on FreeBSD to sponser work like
> the above to happen ?
> Looks to me like it would be beneficial to all parties..
> </soabbox>

If we had the $$ to do so I certainly would.

-- 
Paul Richards <paul_at_freebsd-services.com>
FreeBSD Services Ltd