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([2620:10d:c093:600::2:c503]) by smtp.gmail.com with ESMTPSA id s5sm12141285edi.93.2021.06.22.04.00.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Jun 2021 04:00:36 -0700 (PDT) Subject: Re: [PATCH v3] io_uring: reduce latency by reissueing the operation To: Olivier Langlois , Jens Axboe , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <4deda7761d61c189f4e2581828f852c8a1acb723.1624303174.git.olivier@trillion01.com> From: Pavel Begunkov Message-ID: Date: Tue, 22 Jun 2021 12:00:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <4deda7761d61c189f4e2581828f852c8a1acb723.1624303174.git.olivier@trillion01.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/21/21 8:22 PM, Olivier Langlois wrote: > It is quite frequent that when an operation fails and returns EAGAIN, > the data becomes available between that failure and the call to > vfs_poll() done by io_arm_poll_handler(). > > Detecting the situation and reissuing the operation is much faster > than going ahead and push the operation to the io-wq. Looks good to me, will stamp later after testing it out. > Signed-off-by: Olivier Langlois > --- > fs/io_uring.c | 31 ++++++++++++++++++++++--------- > 1 file changed, 22 insertions(+), 9 deletions(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index fc8637f591a6..5efa67c2f974 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -5152,7 +5152,13 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req, > return mask; > } > > -static bool io_arm_poll_handler(struct io_kiocb *req) > +enum { > + IO_APOLL_OK, > + IO_APOLL_ABORTED, > + IO_APOLL_READY > +}; > + > +static int io_arm_poll_handler(struct io_kiocb *req) > { > const struct io_op_def *def = &io_op_defs[req->opcode]; > struct io_ring_ctx *ctx = req->ctx; > @@ -5162,22 +5168,22 @@ static bool io_arm_poll_handler(struct io_kiocb *req) > int rw; > > if (!req->file || !file_can_poll(req->file)) > - return false; > + return IO_APOLL_ABORTED; > if (req->flags & REQ_F_POLLED) > - return false; > + return IO_APOLL_ABORTED; > if (def->pollin) > rw = READ; > else if (def->pollout) > rw = WRITE; > else > - return false; > + return IO_APOLL_ABORTED; > /* if we can't nonblock try, then no point in arming a poll handler */ > if (!io_file_supports_async(req, rw)) > - return false; > + return IO_APOLL_ABORTED; > > apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC); > if (unlikely(!apoll)) > - return false; > + return IO_APOLL_ABORTED; > apoll->double_poll = NULL; > > req->flags |= REQ_F_POLLED; > @@ -5203,12 +5209,14 @@ static bool io_arm_poll_handler(struct io_kiocb *req) > if (ret || ipt.error) { > io_poll_remove_double(req); > spin_unlock_irq(&ctx->completion_lock); > - return false; > + if (ret) > + return IO_APOLL_READY; > + return IO_APOLL_ABORTED; > } > spin_unlock_irq(&ctx->completion_lock); > trace_io_uring_poll_arm(ctx, req, req->opcode, req->user_data, > mask, apoll->poll.events); > - return true; > + return IO_APOLL_OK; > } > > static bool __io_poll_remove_one(struct io_kiocb *req, > @@ -6437,6 +6445,7 @@ static void __io_queue_sqe(struct io_kiocb *req) > struct io_kiocb *linked_timeout = io_prep_linked_timeout(req); > int ret; > > +issue_sqe: > ret = io_issue_sqe(req, IO_URING_F_NONBLOCK|IO_URING_F_COMPLETE_DEFER); > > /* > @@ -6456,12 +6465,16 @@ static void __io_queue_sqe(struct io_kiocb *req) > io_put_req(req); > } > } else if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) { > - if (!io_arm_poll_handler(req)) { > + switch (io_arm_poll_handler(req)) { > + case IO_APOLL_READY: > + goto issue_sqe; > + case IO_APOLL_ABORTED: > /* > * Queued up for async execution, worker will release > * submit reference when the iocb is actually submitted. > */ > io_queue_async_work(req); > + break; > } > } else { > io_req_complete_failed(req, ret); > -- Pavel Begunkov