commit 13882a82ee1646336c3996c93b4a560a55d2a419
author Clemens Ladisch <clemens@ladisch.de> Mon May 02 09:33:56 2011 +0200
committer Stefan Richter <stefanr@s5r6.in-berlin.de> Tue May 10 22:53:45 2011 +0200
tree 8a144d874a0ac46273a7e2f2dd344458d7eb4bfa
parent f30e6d3e419bfb5540fa82ba7eca01d578556e6b

firewire: optimize iso queueing by setting wake only after the last packet

When queueing iso packets, the run time is dominated by the two
MMIO accesses that set the DMA context's wake bit.  Because most
drivers submit packets in batches, we can save much time by
removing all but the last wakeup.

The internal kernel API is changed to require a call to
fw_iso_context_queue_flush() after a batch of queued packets.
The user space API does not change, so one call to
FW_CDEV_IOC_QUEUE_ISO must specify multiple packets to take
advantage of this optimization.

In my measurements, this patch reduces the time needed to queue
fifty skip packets from userspace to one sixth on a 2.5 GHz CPU,
or to one third at 800 MHz.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>