Pieter Palmers wrote:
Kristian Høgsberg wrote:
Hi,
Here's a new set of patches for the new firewire stack. The changes
since the last set of patches address the issues that were raised on
the list and can be reviewed in detail here:
.. for some reason I didn't get patch 3/4 and 4/4 on the linux1394-devel
list, so I'll reply to this one.
I would suggest a reordering of the interrupt flag checks. Currently the
interrupts that are least likely to occur are checked first. I don't see
why. I would reorder the check such that ISO interrupts are checked
first, as they have the most stringent timing constraints and are most
likely to occur (when using ISO traffic).
All the interrupt handler does is schedule tasklets and they are all handled
before returning to userspace. So not matter how you order them it's going to
take the same time. If you want to defer handling of async traffic to after
your userspace handler has run, you need to schedule a work_struct for
handling the async events.
Having said that, I doubt that the latency between iso interrupt and user
space handler imposed by the irq handler and the tasklets will be a problem.
All the async tasklets do is copy the data out of the DMA buffers, possibly
lookup a corresponding request and eventually call complete() on some struct
completion. The worst case is the bus reset tasklet which does the topology
walk, but even that is pretty fast.
After processing the ISO interrupts (and maybe the Async ones), a bypass
could be inserted to exit the interrupt handler when there are no other
interrupts to be handled. All other interrupts are to report relatively
rare events or errors (error handling still to be added I assume). The
effective run-length of the interrupt handler would be shorter using
such a bypass, especially in the case where there is a lot of ISO traffic.
I'm looking forward to your ISO implementation, and I hope to
incorporate it into FreeBob really fast.
Sounds great, I'll get to the isochronous receive feature as soon as possible.
I'm open to changing the interrupt handling if we can acheive lower latency,
but we need to be able to measure it before we start making changes.
cheers,
Kristian
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