Re: [PATCH 6/6] io_uring: batch completion in prior_task_list

Hao Xu
2021-11-18T10:40:07Z

在 2021/11/18 上午6:55, Pavel Begunkov 写道:
> On 10/29/21 13:22, Hao Xu wrote:
>> In previous patches, we have already gathered some tw with
>> io_req_task_complete() as callback in prior_task_list, let's complete
>> them in batch regardless uring lock. For instance, we are doing simple
>> direct read, most task work will be io_req_task_complete(), with this
>> patch we don't need to hold uring lock there for long time.
>>
>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>> ---
>>   fs/io_uring.c | 52 ++++++++++++++++++++++++++++++++++++++++++---------
>>   1 file changed, 43 insertions(+), 9 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 694195c086f3..565cd0b34f18 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -2166,6 +2166,37 @@ static inline unsigned int
>> io_put_rw_kbuf(struct io_kiocb *req)
>>       return io_put_kbuf(req, req->kbuf);
>>   }
>> +static void handle_prior_tw_list(struct io_wq_work_node *node)
>> +{
>> +    struct io_ring_ctx *ctx = NULL;
>> +
>> +    do {
>> +        struct io_wq_work_node *next = node->next;
>> +        struct io_kiocb *req = container_of(node, struct io_kiocb,
>> +                            io_task_work.node);
>> +        if (req->ctx != ctx) {
>> +            if (ctx) {
>> +                io_commit_cqring(ctx);
>> +                spin_unlock(&ctx->completion_lock);
>> +                io_cqring_ev_posted(ctx);
>> +                percpu_ref_put(&ctx->refs);
>> +            }
>> +            ctx = req->ctx;
>> +            percpu_ref_get(&ctx->refs);
>> +            spin_lock(&ctx->completion_lock);
>> +        }
>> +        __io_req_complete_post(req, req->result, io_put_rw_kbuf(req));
>> +        node = next;
>> +    } while (node);
>> +
>> +    if (ctx) {
>> +        io_commit_cqring(ctx);
>> +        spin_unlock(&ctx->completion_lock);
>> +        io_cqring_ev_posted(ctx);
>> +        percpu_ref_put(&ctx->refs);
>> +    }
>> +}
>> +
>>   static void handle_tw_list(struct io_wq_work_node *node, struct
>> io_ring_ctx **ctx, bool *locked)
>>   {
>>       do {
>> @@ -2193,25 +2224,28 @@ static void tctx_task_work(struct
>> callback_head *cb)
>>                             task_work);
>>       while (1) {
>> -        struct io_wq_work_node *node;
>> -        struct io_wq_work_list *merged_list;
>> +        struct io_wq_work_node *node1, *node2;
>> -        if (!tctx->prior_task_list.first &&
>> -            !tctx->task_list.first && locked)
>> +        if (!tctx->task_list.first &&
>> +            !tctx->prior_task_list.first && locked)
>>               io_submit_flush_completions(ctx);
>>           spin_lock_irq(&tctx->task_lock);
>> -        merged_list = wq_list_merge(&tctx->prior_task_list,
>> &tctx->task_list);
>> -        node = merged_list->first;
>> +        node1 = tctx->prior_task_list.first;
>> +        node2 = tctx->task_list.first;
>>           INIT_WQ_LIST(&tctx->task_list);
>>           INIT_WQ_LIST(&tctx->prior_task_list);
>> -        if (!node)
>> +        if (!node2 && !node1)
>>               tctx->task_running = false;
>>           spin_unlock_irq(&tctx->task_lock);
>> -        if (!node)
>> +        if (!node2 && !node1)
>>               break;
>> -        handle_tw_list(node, &ctx, &locked);
>> +        if (node1)
>> +            handle_prior_tw_list(node1);
>
> IIUC, it moves all IRQ rw completions to this new path even when we already
> have the lock. One concern is that io_submit_flush_completions() is better
> optimised. Should probably be visible for one threaded apps and a bunch of
> other cases.
>
> How about a combined scheme? if we can grab the lock, go through the old
> path, otherwise handle_prior_tw_list(). The rest looks good, will formally
> review once we deal with this one.
Thanks Pavel, I'll look into this patchset soon after
finishing some tests to my io-wq patchset.
>
>> +
>> +        if (node2)
>> +            handle_tw_list(node2, &ctx, &locked);
>>           cond_resched();
>>       }
>>
>