On 11/22/24 17:11, Jens Axboe wrote:
On 11/22/24 10:07 AM, Pavel Begunkov wrote:
On 11/22/24 16:12, Jens Axboe wrote:
...
static inline void io_req_local_work_add(struct io_kiocb *req,
struct io_ring_ctx *ctx,
- unsigned flags)
+ unsigned tw_flags)
{
- unsigned nr_wait, nr_tw, nr_tw_prev;
- struct llist_node *head;
+ unsigned nr_tw, nr_tw_prev, nr_wait;
+ unsigned long flags;
/* See comment above IO_CQ_WAKE_INIT */
BUILD_BUG_ON(IO_CQ_WAKE_FORCE <= IORING_MAX_CQ_ENTRIES);
/*
- * We don't know how many reuqests is there in the link and whether
- * they can even be queued lazily, fall back to non-lazy.
+ * We don't know how many requests are in the link and whether they can
+ * even be queued lazily, fall back to non-lazy.
*/
if (req->flags & (REQ_F_LINK | REQ_F_HARDLINK))
- flags &= ~IOU_F_TWQ_LAZY_WAKE;
+ tw_flags &= ~IOU_F_TWQ_LAZY_WAKE;
- guard(rcu)();
protects against ctx->task deallocation, see a comment in
io_ring_exit_work() -> synchronize_rcu()
Yeah that's just an editing mistake.
+ spin_lock_irqsave(&ctx->work_lock, flags);
+ wq_list_add_tail(&req->io_task_work.work_node, &ctx->work_list);
+ nr_tw_prev = ctx->work_items++;
Is there a good reason why it changes the semantics of
what's stored across adds? It was assigning a corrected
nr_tw, this one will start heavily spamming with wake_up()
in some cases.
Not sure I follow, how so? nr_tw_prev will be the previous count, just
like before. Except we won't need to dig into the list to find it, we
have it readily available. nr_tw will be the current code, or force wake
if needed. As before.
The problem is what it stores, not how and where. Before req->nr_tw
could've been set to IO_CQ_WAKE_FORCE, in which case following
requests are not going to attempt waking up the task, now work_items
is just a counter.
Let's say you've got a bunch of non-lazy adds coming close to each
other. The first sets IO_CQ_WAKE_FORCE and wakes the task, and
others just queue themselves in the list. Now, every single one
of them will try to wake_up() as long as ->cq_wait_nr is large
enough.
--
Pavel Begunkov
