From: Jens Axboe <axboe@kernel.dk>
To: Jonathan Corbet <corbet@lwn.net>
Cc: linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
linux-block@vger.kernel.org, linux-arch@vger.kernel.org,
hch@lst.de, jmoyer@redhat.com, avi@scylladb.com
Subject: Re: [PATCH 05/16] Add io_uring IO interface
Date: Tue, 15 Jan 2019 09:55:32 -0700 [thread overview]
Message-ID: <5e1fe0b7-7998-d15d-267b-4dbbc01b0b53@kernel.dk> (raw)
In-Reply-To: <20190115095134.6286b7d6@lwn.net>
On 1/15/19 9:51 AM, Jonathan Corbet wrote:
> On Mon, 14 Jan 2019 19:55:20 -0700
> Jens Axboe <axboe@kernel.dk> wrote:
>
> So the [0/16] cover letter seems to have gone astray this time?
It did go out, but I forgot to add a Subject line to it...
https://marc.info/?l=linux-block&m=154752095709422&w=2
>> The submission queue (SQ) and completion queue (CQ) rings are shared
>> between the application and the kernel. This eliminates the need to
>> copy data back and forth to submit and complete IO.
>>
>> IO submissions use the io_uring_sqe data structure, and completions
>> are generated in the form of io_uring_sqe data structures. The SQ
>> ring is an index into the io_uring_sqe array, which makes it possible
>> to submit a batch of IOs without them being contiguous in the ring.
>> The CQ ring is always contiguous, as completion events are inherently
>> unordered and can point to any io_uring_iocb.
>>
>> Two new system calls are added for this:
>>
>> io_uring_setup(entries, iovecs, params)
>> Sets up a context for doing async IO. On success, returns a file
>> descriptor that the application can mmap to gain access to the
>> SQ ring, CQ ring, and io_uring_iocbs.
>
> Looking at the code, it would appear that the "iovecs" parameter doesn't
> actually exist.
Indeed, need to update that commit message. and io_uring_iocbs should
now be io_uring_sqes.
The iovec/file registration is done through io_uring_register(2).
>> io_uring_enter(fd, to_submit, min_complete, flags)
>> Initiates IO against the rings mapped to this fd, or waits for
>> them to complete, or both The behavior is controlled by the
>> parameters passed in. If 'min_complete' is non-zero, then we'll
>> try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
>> kernel will wait for 'min_complete' events, if they aren't
>> already available.
>
> I feel like I'm missing something here. Rather than have the
> IORING_ENTER_GETEVENTS flag, why not just wait if min_complete > 0 ?
For polled IO, it's useful to be able to check if we have events that
can be readily reaped. If min_complete > 0, then you're asking the
interface to wait/poll for these events. IORING_ENTER_GETEVENTS +
min_complete == 0 is a valid combination to just reap events that are
already completed.
--
Jens Axboe
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WARNING: multiple messages have this Message-ID (diff)
From: Jens Axboe <axboe@kernel.dk>
To: Jonathan Corbet <corbet@lwn.net>
Cc: linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
linux-block@vger.kernel.org, linux-arch@vger.kernel.org,
hch@lst.de, jmoyer@redhat.com, avi@scylladb.com
Subject: Re: [PATCH 05/16] Add io_uring IO interface
Date: Tue, 15 Jan 2019 09:55:32 -0700 [thread overview]
Message-ID: <5e1fe0b7-7998-d15d-267b-4dbbc01b0b53@kernel.dk> (raw)
Message-ID: <20190115165532.nAI1yQstRKPUNCqDQ59HVXSwb5ZtdPn59UCstQdDJg0@z> (raw)
In-Reply-To: <20190115095134.6286b7d6@lwn.net>
On 1/15/19 9:51 AM, Jonathan Corbet wrote:
> On Mon, 14 Jan 2019 19:55:20 -0700
> Jens Axboe <axboe@kernel.dk> wrote:
>
> So the [0/16] cover letter seems to have gone astray this time?
It did go out, but I forgot to add a Subject line to it...
https://marc.info/?l=linux-block&m=154752095709422&w=2
>> The submission queue (SQ) and completion queue (CQ) rings are shared
>> between the application and the kernel. This eliminates the need to
>> copy data back and forth to submit and complete IO.
>>
>> IO submissions use the io_uring_sqe data structure, and completions
>> are generated in the form of io_uring_sqe data structures. The SQ
>> ring is an index into the io_uring_sqe array, which makes it possible
>> to submit a batch of IOs without them being contiguous in the ring.
>> The CQ ring is always contiguous, as completion events are inherently
>> unordered and can point to any io_uring_iocb.
>>
>> Two new system calls are added for this:
>>
>> io_uring_setup(entries, iovecs, params)
>> Sets up a context for doing async IO. On success, returns a file
>> descriptor that the application can mmap to gain access to the
>> SQ ring, CQ ring, and io_uring_iocbs.
>
> Looking at the code, it would appear that the "iovecs" parameter doesn't
> actually exist.
Indeed, need to update that commit message. and io_uring_iocbs should
now be io_uring_sqes.
The iovec/file registration is done through io_uring_register(2).
>> io_uring_enter(fd, to_submit, min_complete, flags)
>> Initiates IO against the rings mapped to this fd, or waits for
>> them to complete, or both The behavior is controlled by the
>> parameters passed in. If 'min_complete' is non-zero, then we'll
>> try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
>> kernel will wait for 'min_complete' events, if they aren't
>> already available.
>
> I feel like I'm missing something here. Rather than have the
> IORING_ENTER_GETEVENTS flag, why not just wait if min_complete > 0 ?
For polled IO, it's useful to be able to check if we have events that
can be readily reaped. If min_complete > 0, then you're asking the
interface to wait/poll for these events. IORING_ENTER_GETEVENTS +
min_complete == 0 is a valid combination to just reap events that are
already completed.
--
Jens Axboe
next prev parent reply other threads:[~2019-01-15 16:55 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 2:55 (unknown), Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 01/16] fs: add an iopoll method to struct file_operations Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 02/16] block: wire up block device iopoll method Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 03/16] block: add bio_set_polled() helper Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 04/16] iomap: wire up the iopoll method Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 05/16] Add io_uring IO interface Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 16:51 ` Jonathan Corbet
2019-01-15 16:51 ` Jonathan Corbet
2019-01-15 16:55 ` Jens Axboe [this message]
2019-01-15 16:55 ` Jens Axboe
2019-01-15 17:26 ` Jens Axboe
2019-01-15 17:26 ` Jens Axboe
2019-01-16 10:41 ` Arnd Bergmann
2019-01-16 10:41 ` Arnd Bergmann
2019-01-16 11:00 ` Arnd Bergmann
2019-01-16 11:00 ` Arnd Bergmann
2019-01-16 15:12 ` Jens Axboe
2019-01-16 15:12 ` Jens Axboe
2019-01-16 15:16 ` Arnd Bergmann
2019-01-16 15:16 ` Arnd Bergmann
2019-01-16 15:25 ` Jens Axboe
2019-01-16 15:25 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 06/16] io_uring: add fsync support Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 07/16] io_uring: support for IO polling Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 08/16] io_uring: add submission side request cache Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 09/16] fs: add fget_many() and fput_many() Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 10/16] io_uring: use fget/fput_many() for file references Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 11/16] io_uring: batch io_kiocb allocation Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 12/16] block: implement bio helper to add iter bvec pages to bio Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 13/16] io_uring: add support for pre-mapped user IO buffers Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-16 10:53 ` Arnd Bergmann
2019-01-16 15:14 ` Jens Axboe
2019-01-16 15:14 ` Jens Axboe
2019-01-16 15:32 ` Jens Axboe
2019-01-16 15:32 ` Jens Axboe
2019-01-16 15:41 ` Arnd Bergmann
2019-01-16 15:47 ` Jens Axboe
2019-01-16 15:47 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 14/16] io_uring: add submission polling Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 15/16] io_uring: add file registration Jens Axboe
2019-01-15 2:55 ` Jens Axboe
2019-01-16 10:45 ` Arnd Bergmann
2019-01-16 10:45 ` Arnd Bergmann
2019-01-16 15:15 ` Jens Axboe
2019-01-16 15:15 ` Jens Axboe
2019-01-15 2:55 ` [PATCH 16/16] io_uring: add io_uring_event cache hit information Jens Axboe
2019-01-15 2:55 ` Jens Axboe
-- strict thread matches above, loose matches on Subject: below --
2019-01-12 21:29 [PATCHSET v3] io_uring IO interface Jens Axboe
2019-01-12 21:30 ` [PATCH 05/16] Add " Jens Axboe
2019-01-12 21:30 ` Jens Axboe
2019-01-08 16:56 [PATCHSET v1] " Jens Axboe
2019-01-08 16:56 ` [PATCH 05/16] Add " Jens Axboe
2019-01-08 16:56 ` Jens Axboe
2019-01-09 12:10 ` Christoph Hellwig
2019-01-09 15:53 ` Jens Axboe
2019-01-09 15:53 ` Jens Axboe
2019-01-09 18:30 ` Christoph Hellwig
2019-01-09 18:30 ` Christoph Hellwig
2019-01-09 20:07 ` Jens Axboe
2019-01-09 20:07 ` Jens Axboe
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