Re: [PATCH v3 2/2] selftests: ublk: add rq_affinity test

[Ming Lei <tom.leiming@gmail.com>]

On Mon, Oct 26, 2026 at 02:06:19PM +0200, Yoav Cohen wrote:
> Add UBLK_F_SUPPORT_RQ_AFFINITY to kublk's feature table and a
> --rq_affinity flag to request it at ADD_DEV time, and add
> test_generic_18.sh: writes and verifies data on a loop device with
> I/O pinned to one CPU while cycling rq_affinity through 0, 1 and 2.
> Skipped on kernels without UBLK_F_SUPPORT_RQ_AFFINITY.
> 
> Signed-off-by: Yoav Cohen <yoav@nvidia.com>
> ---
>  tools/testing/selftests/ublk/Makefile         |  1 +
>  tools/testing/selftests/ublk/kublk.c          |  6 ++-
>  .../testing/selftests/ublk/test_generic_18.sh | 42 +++++++++++++++++++
>  3 files changed, 48 insertions(+), 1 deletion(-)
>  create mode 100755 tools/testing/selftests/ublk/test_generic_18.sh

...

> diff --git a/tools/testing/selftests/ublk/test_generic_18.sh b/tools/testing/selftests/ublk/test_generic_18.sh
> new file mode 100755
> index 000000000000..c899a5bf0364
> --- /dev/null
> +++ b/tools/testing/selftests/ublk/test_generic_18.sh

Please rebase on latest linus tree and rename to test_generic_19.sh, 18 has
been taken already.

> @@ -0,0 +1,42 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +
> +. "$(cd "$(dirname "$0")" && pwd)"/test_common.sh
> +
> +ERR_CODE=0
> +
> +if ! _have_program fio; then
> +	exit "$UBLK_SKIP_CODE"
> +fi
> +
> +if ! _have_feature "SUPPORT_RQ_AFFINITY"; then
> +	exit "$UBLK_SKIP_CODE"
> +fi
> +
> +_prep_test "loop" "write and verify I/O across rq_affinity settings"
> +
> +_create_backfile 0 256M
> +
> +dev_id=$(_add_ublk_dev -t loop --rq_affinity "${UBLK_BACKFILES[0]}")
> +_check_add_dev $TID $?
> +
> +rq_affinity_path=/sys/block/ublkb"${dev_id}"/queue/rq_affinity
> +
> +for affinity in 0 1 2; do
> +	echo "${affinity}" > "${rq_affinity_path}"
> +
> +	# Pin submission to a single CPU so rq_affinity has somewhere to
> +	# redirect completion to.
> +	taskset -c 0 fio --name=verify --rw=randwrite --direct=1 \
> +		--ioengine=libaio --bs=8k --iodepth=32 --verify=crc32c \
> +		--do_verify=1 --verify_state_save=0 \
> +		--filename=/dev/ublkb"${dev_id}" --size=256M > /dev/null

This doesn't cover the remote completion path: kublk pins the queue 0
thread to the first CPU of its hctx mask, which is CPU 0 here, so the
request is completed inline for all three rq_affinity values.

Please use single queue and submit from the last CPU in
/sys/block/ublkb${dev_id}/mq/0/cpu_list, then rq_affinity=2 always takes
the IPI path. I verified that way across copy, zero copy, auto_zc, user
copy and batch modes, all pass.



Thanks, 
Ming