On 11/6/2019 11:36 AM, Bob Liu wrote:
> On 11/6/19 5:22 AM, Pavel Begunkov wrote:
>> After a call to io_submit_sqe(), it's already known whether it needs
>> to queue a link or not. Do it there, as it's simplier and doesn't keep
>> an extra variable across the loop.
>>
>> Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
>> ---
>> fs/io_uring.c | 22 ++++++++++------------
>> 1 file changed, 10 insertions(+), 12 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index ebe2a4edd644..82c2da99cb5c 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -2687,7 +2687,6 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
>> struct io_submit_state state, *statep = NULL;
>> struct io_kiocb *link = NULL;
>> struct io_kiocb *shadow_req = NULL;
>> - bool prev_was_link = false;
>> int i, submitted = 0;
>> bool mm_fault = false;
>>
>> @@ -2710,17 +2709,6 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
>> }
>> }
>>
>> - /*
>> - * If previous wasn't linked and we have a linked command,
>> - * that's the end of the chain. Submit the previous link.
>> - */
>> - if (!prev_was_link && link) {
>> - io_queue_link_head(ctx, link, &link->submit, shadow_req);
>> - link = NULL;
>> - shadow_req = NULL;
>> - }
>> - prev_was_link = (s.sqe->flags & IOSQE_IO_LINK) != 0;
>> -
>> if (link && (s.sqe->flags & IOSQE_IO_DRAIN)) {
>> if (!shadow_req) {
>> shadow_req = io_get_req(ctx, NULL);
>> @@ -2741,6 +2729,16 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
>> trace_io_uring_submit_sqe(ctx, s.sqe->user_data, true, async);
>> io_submit_sqe(ctx, &s, statep, &link);
>> submitted++;
>> +
>> + /*
>> + * If previous wasn't linked and we have a linked command,
>> + * that's the end of the chain. Submit the previous link.
>> + */
>> + if (!(s.sqe->flags & IOSQE_IO_LINK) && link)
> The behavior changed to 'current seq' instead of previous after dropping prev_was_link?
>
The old behaviour was to remember @prev_was_link for current sqe, and
use at the beginning of the next iteration, where it becomes
"previous/last sqe". See, prev_was_link was set after io_queue_link_head.
If @i is iteration idx, then timeline was:
i: sqe[i-1].is_link -> io_queue_link_head() # if (prev_was_link)
i: sqe[i].is_link = prev_was_link = (sqe[i].flags & LINK)
i+1: sqe[i].is_link -> io_queue_link_head() # if (prev_was_link)
i+1: sqe[i+1].is_link = ...
After the change, it's done at the same loop iteration by swapping order
of checking @prev_was_link and io_queue_link_head().
i: sqe[i].is_link = ...
i: sqe[i].is_link -> io_queue_link_head()
i+1: sqe[i+1].is_link = ...
i+1: sqe[i+1].is_link -> io_queue_link_head()
Shouldn't change the behavior, if I'm not missing something.
>> + io_queue_link_head(ctx, link, &link->submit, shadow_req);
>> + link = NULL;
>> + shadow_req = NULL;
>> + }
>> }
>>
>> if (link)
>>
>
