linux-kernel - [PATCH v5 0/4] ublk: decouple server threads from hctxs

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Message-Id: <20250416-ublk_task_per_io-v5-0-9261ad7bff20@purestorage.com>
Date: Wed, 16 Apr 2025 13:46:04 -0600
From: Uday Shankar <ushankar@...estorage.com>
To: Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...nel.dk>, 
 Caleb Sander Mateos <csander@...estorage.com>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Uday Shankar <ushankar@...estorage.com>
Subject: [PATCH v5 0/4] ublk: decouple server threads from hctxs

This patch set aims to allow ublk server threads to better balance load
amongst themselves by decoupling server threads from ublk queues/hctxs,
so that multiple threads can service I/Os from a single hctx.

Signed-off-by: Uday Shankar <ushankar@...estorage.com>
---
Changes in v5:
- Set io->task before ublk_mark_io_ready (Caleb Sander Mateos)
- Set io->task atomically, read it atomically when needed
- Return 0 on success from command-specific helpers in
  __ublk_ch_uring_cmd (Caleb Sander Mateos)
- Rename ublk_handle_need_get_data to ublk_get_data (Caleb Sander
  Mateos)
- Link to v4: https://lore.kernel.org/r/20250415-ublk_task_per_io-v4-0-54210b91a46f@purestorage.com

Changes in v4:
- Drop "ublk: properly serialize all FETCH_REQs" since Ming is taking it
  in another set
- Prevent data races by marking data structures which should be
  read-only in the I/O path as const (Ming Lei)
- Link to v3: https://lore.kernel.org/r/20250410-ublk_task_per_io-v3-0-b811e8f4554a@purestorage.com

Changes in v3:
- Check for UBLK_IO_FLAG_ACTIVE on I/O again after taking lock to ensure
  that two concurrent FETCH_REQs on the same I/O can't succeed (Caleb
  Sander Mateos)
- Link to v2: https://lore.kernel.org/r/20250408-ublk_task_per_io-v2-0-b97877e6fd50@purestorage.com

Changes in v2:
- Remove changes split into other patches
- To ease error handling/synchronization, associate each I/O (instead of
  each queue) to the last task that issues a FETCH_REQ against it. Only
  that task is allowed to operate on the I/O.
- Link to v1: https://lore.kernel.org/r/20241002224437.3088981-1-ushankar@purestorage.com

---
Uday Shankar (4):
      ublk: require unique task per io instead of unique task per hctx
      ublk: mark ublk_queue as const for ublk_commit_and_fetch
      ublk: mark ublk_queue as const for ublk_register_io_buf
      ublk: mark ublk_queue as const for ublk_handle_need_get_data

 drivers/block/ublk_drv.c | 205 +++++++++++++++++++++++------------------------
 1 file changed, 100 insertions(+), 105 deletions(-)
---
base-commit: d3b4b25e363e4ce193e6103e64f7de12b96668b9
change-id: 20250408-ublk_task_per_io-c693cf608d7a

Best regards,
-- 
Uday Shankar <ushankar@...estorage.com>