Re: [PATCH 2/3] block: enable bio caching use for passthru IO

On 8/7/22 12:08 PM, Kanchan Joshi wrote:

On Sat, Aug 06, 2022 at 09:20:03AM -0600, Jens Axboe wrote:

quoted

bdev based polled O_DIRECT is currently quite a bit faster than
passthru on the same device, and one of the reaons is that we're not
able to use the bio caching for passthru IO.

If REQ_POLLED is set on the request, use the fs bio set for grabbing a
bio from the caches, if available. This saves 5-6% of CPU over head
for polled passthru IO.

For passthru path, bio is always freed in the task-context (and not in
irq) so must this be tied to polled-io only?

Right, that's why it's tied to polled. If polling gets cleared, then it
will be freed normally on completion rather than inserted into the
cache.

I do have patches for irq bio caching too, that'll work fine with
io_uring:

https://git.kernel.dk/cgit/linux-block/commit/?h=perf-wip&id=ab3d4371227a34a5561e4d594a17baaad03bf1b7

I'll post that too, would be nice if we can figure out a clean way to do
this. I have posted it before, iirc.

-- 
Jens Axboe