Re: [PATCH for-next v3 0/3] implement pcpu bio caching for IRQ I/O

[Kanchan Joshi]

On Fri, Oct 21, 2022 at 11:34:04AM +0100, Pavel Begunkov wrote:
> Add bio pcpu caching for normal / IRQ-driven I/O extending REQ_ALLOC_CACHE,
> which was limited to iopoll. 

So below comment (stating process context as MUST) can also be removed as
part of this series now?

495  * If REQ_ALLOC_CACHE is set, the final put of the bio MUST be done from process
496  * context, not hard/soft IRQ.
497  *
498  * Returns: Pointer to new bio on success, NULL on failure.
499  */
500 struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
501                              blk_opf_t opf, gfp_t gfp_mask,
502                              struct bio_set *bs)
503 {

> t/io_uring with an Optane SSD setup showed +7%
> for batches of 32 requests and +4.3% for batches of 8.
>
> IRQ, 128/32/32, cache off
> IOPS=59.08M, BW=28.84GiB/s, IOS/call=31/31
> IOPS=59.30M, BW=28.96GiB/s, IOS/call=32/32
> IOPS=59.97M, BW=29.28GiB/s, IOS/call=31/31
> IOPS=59.92M, BW=29.26GiB/s, IOS/call=32/32
> IOPS=59.81M, BW=29.20GiB/s, IOS/call=32/31
>
> IRQ, 128/32/32, cache on
> IOPS=64.05M, BW=31.27GiB/s, IOS/call=32/31
> IOPS=64.22M, BW=31.36GiB/s, IOS/call=32/32
> IOPS=64.04M, BW=31.27GiB/s, IOS/call=31/31
> IOPS=63.16M, BW=30.84GiB/s, IOS/call=32/32
>
> IRQ, 32/8/8, cache off
> IOPS=50.60M, BW=24.71GiB/s, IOS/call=7/8
> IOPS=50.22M, BW=24.52GiB/s, IOS/call=8/7
> IOPS=49.54M, BW=24.19GiB/s, IOS/call=8/8
> IOPS=50.07M, BW=24.45GiB/s, IOS/call=7/7
> IOPS=50.46M, BW=24.64GiB/s, IOS/call=8/8
>
> IRQ, 32/8/8, cache on
> IOPS=51.39M, BW=25.09GiB/s, IOS/call=8/7
> IOPS=52.52M, BW=25.64GiB/s, IOS/call=7/8
> IOPS=52.57M, BW=25.67GiB/s, IOS/call=8/8
> IOPS=52.58M, BW=25.67GiB/s, IOS/call=8/7
> IOPS=52.61M, BW=25.69GiB/s, IOS/call=8/8
>
> The next step will be turning it on for other users, hopefully by default.
> The only restriction we currently have is that the allocations can't be
> done from non-irq context and so needs auditing.

Isn't allocation (of bio) happening in non-irq context already?

And
Reviewed-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>