On 3/11/23 20:45, Pavel Begunkov wrote:
On 3/11/23 17:24, Jens Axboe wrote:
On 3/10/23 12:04?PM, Pavel Begunkov wrote:
io_uring extensively uses task_work, but when a task is waiting
for multiple CQEs it causes lots of rescheduling. This series
is an attempt to optimise it and be a base for future improvements.
For some zc network tests eventually waiting for a portion of
buffers I've got 10x descrease in the number of context switches,
which reduced the CPU consumption more than twice (17% -> 8%).
It also helps storage cases, while running fio/t/io_uring against
a low performant drive it got 2x descrease of the number of context
switches for QD8 and ~4 times for QD32.
Not for inclusion yet, I want to add an optimisation for when
waiting for 1 CQE.
Ran this on the usual peak benchmark, using IRQ. IOPS is around ~70M for
that, and I see context rates of around 8.1-8.3M/sec with the current
kernel.
Applied the two patches, but didn't see much of a change? Performance is
about the same, and cx rate ditto. Confused... As you probably know,
this test waits for 32 ios at the time.
If I'd to guess it already has perfect batching, for which case
the patch does nothing. Maybe it's due to SSD coalescing +
small ro I/O + consistency and small latencies of Optanes,
or might be on the scheduling and the kernel side to be slow
to react.
And if that's that, I have to note that it's quite a sterile
case, the last time I asked the usual batching we're currently
getting for networking cases is 1-2.
--
Pavel Begunkov
