The drivers we have that don't dequeue all the CQEs are doing
something like NAPI polling and have other mechanisms to guarentee
progress. Don't copy something like budget without copying the other
mechanisms :)
OK, that makes total sense. Thanks for clarifying.
IIRC NAPI is soft-IRQ which chuck is trying to avoid.
Chuck, I think I was the one that commented on this. I observed a
situation in iser where the polling loop kept going continuously
without ever leaving the soft-IRQ context (high workload obviously).
In addition to the polling loop hogging the CPU, other CQs with the
same IRQ assignment were starved. So I suggested you should take care
of it in xprtrdma as well.
The correct approach is NAPI. There is an equivalent for storage which
is called blk_iopoll (block/blk-iopool.c) which sort of has nothing
specific to block devices (also soft-IRQ context). I have attempted to
convert iser to use it, but I got some unpredictable latency jitters so
I stopped and didn't get a chance to pick it up ever since.
I still think that draining the CQ without respecting a quota is
wrong, even if driverX has a glitch there.
Sagi.
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