On 6/9/22 23:06, Jens Axboe wrote:
On 6/9/22 4:32 AM, Hao Xu wrote:
On 6/9/22 18:19, Jens Axboe wrote:
On 6/9/22 4:14 AM, Hao Xu wrote:
On 6/9/22 18:06, Jens Axboe wrote:
On 6/9/22 1:53 AM, Hao Xu wrote:
Hi all,
I haven't done tests to demonstrate it. It is for partial io case, we
don't consume/release the buffer before arm_poll in ring-mapped mode.
But seems we should? Otherwise ring head isn't moved and other requests
may take that buffer. What do I miss?
On vacation this week, so can't take a look at the code. But the
principle is precisely not to consume the buffer if we arm poll, because
then the next one can grab it instead. We don't want to consume a buffer
over poll, as that defeats the purpose of a provided buffer. It should
be grabbed and consumed only if we can use it right now.
Hence the way it should work is that we DON'T consume the buffer in this
case, and that someone else can just use it. At the same time, we should
ensure that we grab a NEW buffer for this case, whenever the poll
If we grab a new buffer for it, then we have to copy the data since we
have done partial io...this also defeats the purpose of this feature.
For partial IO, we never drop the buffer. See the logic in
io_kbuf_recycle(). It should be as follows:
Yea, in io_kbuf_recycle(), if it's partial io, we just return. For
legacy mode, this means we keep the buffer. For ring-mapped mode, this
means we then release the uring_lock without moving the ring->head,
and then other requests may take that buffer which is in use..
And next time we do (for example) recv(), we lost the data which we got
at the previous time.
Do I miss something?
If we don't commit for ring mapped buffers, then yeah that's definitely
a bug. Please send a fix :-)
Pavel can take care of it this week.
I'll send a patch tomorrow.
Thanks,
Hao
