linux-kernel - Re: [PATCH 3/3] io_uring/uring_cmd: avoid double indirect call in task work dispatch

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Message-ID: <CADUfDZoMJ26nS9qzk1ACKX_MXkSpBy1kEEkekZoHyCrHtrGZRg@mail.gmail.com>
Date: Thu, 23 Oct 2025 12:12:06 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: Christoph Hellwig <hch@....de>
Cc: Jens Axboe <axboe@...nel.dk>, Miklos Szeredi <miklos@...redi.hu>, Ming Lei <ming.lei@...hat.com>, 
	Keith Busch <kbusch@...nel.org>, Sagi Grimberg <sagi@...mberg.me>, Chris Mason <clm@...com>, 
	David Sterba <dsterba@...e.com>, io-uring@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org, 
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] io_uring/uring_cmd: avoid double indirect call in
 task work dispatch

On Thu, Oct 23, 2025 at 6:40 AM Christoph Hellwig <hch@....de> wrote:
>
> On Wed, Oct 22, 2025 at 05:13:26PM -0600, Caleb Sander Mateos wrote:
> > io_uring task work dispatch makes an indirect call to struct io_kiocb's
> > io_task_work.func field to allow running arbitrary task work functions.
> > In the uring_cmd case, this calls io_uring_cmd_work(), which immediately
> > makes another indirect call to struct io_uring_cmd's task_work_cb field.
> > Introduce a macro DEFINE_IO_URING_CMD_TASK_WORK() to define a
> > io_req_tw_func_t function wrapping an io_uring_cmd_tw_t. Convert the
> > io_uring_cmd_tw_t function to the io_req_tw_func_t function in
> > io_uring_cmd_complete_in_task() and io_uring_cmd_do_in_task_lazy().
> > Use DEFINE_IO_URING_CMD_TASK_WORK() to define a io_req_tw_func_t
> > function for each existing io_uring_cmd_tw_t function. Now uring_cmd
> > task work dispatch makes a single indirect call to the io_req_tw_func_t
> > wrapper function, which can inline the io_uring_cmd_tw_t function. This
> > also allows removing the task_work_cb field from struct io_uring_cmd,
> > freeing up some additional storage space.
>
> Please just open code the logic instead of the symbol-hiding multi-level
> macro indirection.  Everyone who will have to touch the code in the
> future will thank you.

Sure, I can send out a v2 with that. My concern was that
io_kiocb_to_cmd() isn't really meant to be used outside the io_uring
internals. But I agree hiding the function definition in a macro is
less than ideal.

Thanks,
Caleb