Jens Axboe <axboe@xxxxxxxxx> writes:
> It can be quite expensive for the fast paths to deference
> req->task->io_uring->in_cancel for the (very) unlikely scenario that
> we're currently undergoing cancelations.
>
> Add a ctx bit to indicate if we're currently canceling or not, so that
> the hot path may check this rather than dip into the remote task
> state.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> include/linux/io_uring_types.h | 2 ++
> io_uring/io_uring.c | 44 ++++++++++++++++++++++++++++++++--
> 2 files changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> index 00689c12f6ab..42d704adb9c6 100644
> --- a/include/linux/io_uring_types.h
> +++ b/include/linux/io_uring_types.h
> @@ -211,6 +211,8 @@ struct io_ring_ctx {
> enum task_work_notify_mode notify_method;
> struct io_rings *rings;
> struct task_struct *submitter_task;
> + /* local ctx cache of task cancel state */
> + unsigned long in_cancel;
minor nit:
even though the real tctx value is ulong, the cache could just be a bitfield
alongside the many others in this structure. you only care if it is >0
or 0 when peeking the cache.
either way,
Reviewed-by: Gabriel Krisman Bertazi <krisman@xxxxxxx>
> struct percpu_ref refs;
> } ____cacheline_aligned_in_smp;
>
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 64e07df034d1..0fcb532db1fc 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -3192,6 +3192,46 @@ static s64 tctx_inflight(struct io_uring_task *tctx, bool tracked)
> return percpu_counter_sum(&tctx->inflight);
> }
>
> +static __cold void io_uring_dec_cancel(struct io_uring_task *tctx,
> + struct io_sq_data *sqd)
> +{
> + if (!atomic_dec_return(&tctx->in_cancel))
> + return;
> +
> + if (!sqd) {
> + struct io_tctx_node *node;
> + unsigned long index;
> +
> + xa_for_each(&tctx->xa, index, node)
> + clear_bit(0, &node->ctx->in_cancel);
> + } else {
> + struct io_ring_ctx *ctx;
> +
> + list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
> + clear_bit(0, &ctx->in_cancel);
> + }
> +}
> +
> +static __cold void io_uring_inc_cancel(struct io_uring_task *tctx,
> + struct io_sq_data *sqd)
> +{
> + if (atomic_inc_return(&tctx->in_cancel) != 1)
> + return;
> +
> + if (!sqd) {
> + struct io_tctx_node *node;
> + unsigned long index;
> +
> + xa_for_each(&tctx->xa, index, node)
> + set_bit(0, &node->ctx->in_cancel);
> + } else {
> + struct io_ring_ctx *ctx;
> +
> + list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
> + set_bit(0, &ctx->in_cancel);
> + }
> +}
> +
> /*
> * Find any io_uring ctx that this task has registered or done IO on, and cancel
> * requests. @sqd should be not-null IFF it's an SQPOLL thread cancellation.
> @@ -3210,7 +3250,7 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
> if (tctx->io_wq)
> io_wq_exit_start(tctx->io_wq);
>
> - atomic_inc(&tctx->in_cancel);
> + io_uring_inc_cancel(tctx, sqd);
> do {
> bool loop = false;
>
> @@ -3263,7 +3303,7 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
> * We shouldn't run task_works after cancel, so just leave
> * ->in_cancel set for normal exit.
> */
> - atomic_dec(&tctx->in_cancel);
> + io_uring_dec_cancel(tctx, sqd);
> /* for exec all current's requests should be gone, kill tctx */
> __io_uring_free(current);
> }
--
Gabriel Krisman Bertazi
