Re: [PATCH] io-wq: simplify code in __io_worker_busy

[Pavel Begunkov <asml.silence@gmail.com>]

On 02/04/2021 11:18, Hao Xu wrote:
> leverage xor to simplify code in __io_worker_busy

I don't like hard-coded ^1 because if indexes change it may break.
One option is to leave it to the compiler:

idx = bound : WQ_BOUND ? WQ_UNBOUND;
compl_idx = bound : WQ_UNBOUND ? WQ_BOUND;

Or add a BUILD_BUG_ON() checking that WQ_BOUND and WQ_UNBOUND
are mod 2 complementary.


> 
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
>  fs/io-wq.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index 7434eb40ca8c..f77e4704d7c7 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -292,16 +292,11 @@ static void __io_worker_busy(struct io_wqe *wqe, struct io_worker *worker,
>  	worker_bound = (worker->flags & IO_WORKER_F_BOUND) != 0;
>  	work_bound = (work->flags & IO_WQ_WORK_UNBOUND) == 0;
>  	if (worker_bound != work_bound) {
> +		int index = work_bound ? IO_WQ_ACCT_UNBOUND : IO_WQ_ACCT_BOUND;
>  		io_wqe_dec_running(worker);
> -		if (work_bound) {
> -			worker->flags |= IO_WORKER_F_BOUND;
> -			wqe->acct[IO_WQ_ACCT_UNBOUND].nr_workers--;
> -			wqe->acct[IO_WQ_ACCT_BOUND].nr_workers++;
> -		} else {
> -			worker->flags &= ~IO_WORKER_F_BOUND;
> -			wqe->acct[IO_WQ_ACCT_UNBOUND].nr_workers++;
> -			wqe->acct[IO_WQ_ACCT_BOUND].nr_workers--;
> -		}
> +		worker->flags ^= IO_WORKER_F_BOUND;
> +		wqe->acct[index].nr_workers--;
> +		wqe->acct[index^1].nr_workers++;
>  		io_wqe_inc_running(worker);
>  	 }
>  }
> 

-- 
Pavel Begunkov