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From: Jens Axboe <axboe@kernel.dk>
To: sedat.dilek@gmail.com
Cc: io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	akpm@linux-foundation.org
Subject: Re: [PATCHSET v5 0/12] Add support for async buffered reads
Date: Thu, 28 May 2020 11:06:20 -0600	[thread overview]
Message-ID: <bab2d6f8-4c65-be21-6a8e-29b76c06807d@kernel.dk> (raw)
In-Reply-To: <CA+icZUWfX+QmroE6j74C7o-BdfMF5=6PdYrA=5W_JCKddqkJgQ@mail.gmail.com>

On 5/28/20 11:02 AM, Sedat Dilek wrote:
> On Tue, May 26, 2020 at 10:59 PM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> We technically support this already through io_uring, but it's
>> implemented with a thread backend to support cases where we would
>> block. This isn't ideal.
>>
>> After a few prep patches, the core of this patchset is adding support
>> for async callbacks on page unlock. With this primitive, we can simply
>> retry the IO operation. With io_uring, this works a lot like poll based
>> retry for files that support it. If a page is currently locked and
>> needed, -EIOCBQUEUED is returned with a callback armed. The callers
>> callback is responsible for restarting the operation.
>>
>> With this callback primitive, we can add support for
>> generic_file_buffered_read(), which is what most file systems end up
>> using for buffered reads. XFS/ext4/btrfs/bdev is wired up, but probably
>> trivial to add more.
>>
>> The file flags support for this by setting FMODE_BUF_RASYNC, similar
>> to what we do for FMODE_NOWAIT. Open to suggestions here if this is
>> the preferred method or not.
>>
>> In terms of results, I wrote a small test app that randomly reads 4G
>> of data in 4K chunks from a file hosted by ext4. The app uses a queue
>> depth of 32. If you want to test yourself, you can just use buffered=1
>> with ioengine=io_uring with fio. No application changes are needed to
>> use the more optimized buffered async read.
>>
>> preadv for comparison:
>>         real    1m13.821s
>>         user    0m0.558s
>>         sys     0m11.125s
>>         CPU     ~13%
>>
>> Mainline:
>>         real    0m12.054s
>>         user    0m0.111s
>>         sys     0m5.659s
>>         CPU     ~32% + ~50% == ~82%
>>
>> This patchset:
>>         real    0m9.283s
>>         user    0m0.147s
>>         sys     0m4.619s
>>         CPU     ~52%
>>
>> The CPU numbers are just a rough estimate. For the mainline io_uring
>> run, this includes the app itself and all the threads doing IO on its
>> behalf (32% for the app, ~1.6% per worker and 32 of them). Context
>> switch rate is much smaller with the patchset, since we only have the
>> one task performing IO.
>>
>> Also ran a simple fio based test case, varying the queue depth from 1
>> to 16, doubling every time:
>>
>> [buf-test]
>> filename=/data/file
>> direct=0
>> ioengine=io_uring
>> norandommap
>> rw=randread
>> bs=4k
>> iodepth=${QD}
>> randseed=89
>> runtime=10s
>>
>> QD/Test         Patchset IOPS           Mainline IOPS
>> 1               9046                    8294
>> 2               19.8k                   18.9k
>> 4               39.2k                   28.5k
>> 8               64.4k                   31.4k
>> 16              65.7k                   37.8k
>>
>> Outside of my usual environment, so this is just running on a virtualized
>> NVMe device in qemu, using ext4 as the file system. NVMe isn't very
>> efficient virtualized, so we run out of steam at ~65K which is why we
>> flatline on the patched side (nvme_submit_cmd() eats ~75% of the test app
>> CPU). Before that happens, it's a linear increase. Not shown is context
>> switch rate, which is massively lower with the new code. The old thread
>> offload adds a blocking thread per pending IO, so context rate quickly
>> goes through the roof.
>>
>> The goal here is efficiency. Async thread offload adds latency, and
>> it also adds noticable overhead on items such as adding pages to the
>> page cache. By allowing proper async buffered read support, we don't
>> have X threads hammering on the same inode page cache, we have just
>> the single app actually doing IO.
>>
>> Been beating on this and it's solid for me, and I'm now pretty happy
>> with how it all turned out. Not aware of any missing bits/pieces or
>> code cleanups that need doing.
>>
>> Series can also be found here:
>>
>> https://git.kernel.dk/cgit/linux-block/log/?h=async-buffered.5
>>
>> or pull from:
>>
>> git://git.kernel.dk/linux-block async-buffered.5
>>
> 
> Hi Jens,
> 
> I have pulled linux-block.git#async-buffered.5 on top of Linux v5.7-rc7.
> 
> From first feelings:
> The booting into the system (until sddm display-login-manager) took a
> bit longer.
> The same after login and booting into KDE/Plasma.

There is no difference for "regular" use cases, only io_uring with
buffered reads will behave differently. So I don't think you have longer
boot times due to this.

> I am building/linking with LLVM/Clang/LLD v10.0.1-rc1 on Debian/testing AMD64.
> 
> Here I have an internal HDD (SATA) and my Debian-system is on an
> external HDD connected via USB-3.0.
> Primarily, I use Ext4-FS.
> 
> As said above is the "emotional" side, but I need some technical instructions.
> 
> How can I see Async Buffer Reads is active on a Ext4-FS-formatted partition?

You can't see that. It'll always be available on ext4 with this series,
and you can watch io_uring instances to see if anyone is using it.

> Do I need a special boot-parameter (GRUB line)?
> 
> Do I need to activate some cool variables via sysfs?
> 
> Do I need to pass an option via fstab entry?

No to all of these, you don't need anything to activate it. You need the
program to use io_uring to do buffered reads.

> Are any Async Buffer Reads related linux-kconfig options not set?
> Which make sense?

No kconfig options are needed.

-- 
Jens Axboe


  parent reply	other threads:[~2020-05-28 17:06 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-26 19:51 [PATCHSET v5 0/12] Add support for async buffered reads Jens Axboe
2020-05-26 19:51 ` [PATCH 01/12] block: read-ahead submission should imply no-wait as well Jens Axboe
2020-05-26 19:51 ` [PATCH 02/12] mm: allow read-ahead with IOCB_NOWAIT set Jens Axboe
2020-05-26 20:45   ` Johannes Weiner
2020-05-26 19:51 ` [PATCH 03/12] mm: abstract out wake_page_match() from wake_page_function() Jens Axboe
2020-05-26 21:02   ` Johannes Weiner
2020-06-01 14:16   ` Matthew Wilcox
2020-05-26 19:51 ` [PATCH 04/12] mm: add support for async page locking Jens Axboe
2020-05-26 21:59   ` Johannes Weiner
2020-05-26 22:01     ` Jens Axboe
2020-05-27 16:02       ` Johannes Weiner
2020-06-01 14:26   ` Matthew Wilcox
2020-06-01 17:15     ` Jens Axboe
2020-05-26 19:51 ` [PATCH 05/12] mm: support async buffered reads in generic_file_buffered_read() Jens Axboe
2020-05-26 22:00   ` Johannes Weiner
2020-05-26 19:51 ` [PATCH 06/12] fs: add FMODE_BUF_RASYNC Jens Axboe
2020-05-26 19:51 ` [PATCH 07/12] ext4: flag as supporting buffered async reads Jens Axboe
2020-05-26 19:51 ` [PATCH 08/12] block: flag block devices as supporting IOCB_WAITQ Jens Axboe
2020-05-26 19:51 ` [PATCH 09/12] xfs: flag files as supporting buffered async reads Jens Axboe
2020-05-28 17:53   ` Darrick J. Wong
2020-05-28 19:23     ` Jens Axboe
2020-05-26 19:51 ` [PATCH 10/12] btrfs: " Jens Axboe
2020-05-26 19:57   ` Chris Mason
2020-05-26 19:51 ` [PATCH 11/12] mm: add kiocb_wait_page_queue_init() helper Jens Axboe
2020-05-26 22:01   ` Johannes Weiner
2020-05-26 19:51 ` [PATCH 12/12] io_uring: support true async buffered reads, if file provides it Jens Axboe
     [not found] ` <CA+icZUWfX+QmroE6j74C7o-BdfMF5=6PdYrA=5W_JCKddqkJgQ@mail.gmail.com>
2020-05-28 17:06   ` Jens Axboe [this message]
2020-05-28 17:12     ` [PATCHSET v5 0/12] Add support for async buffered reads Sedat Dilek
2020-05-28 17:14       ` Jens Axboe
2020-05-28 18:20         ` Sedat Dilek
2020-05-29 10:02     ` Sedat Dilek
2020-05-29 11:22       ` Sedat Dilek
2020-05-30 13:36         ` Sedat Dilek
2020-05-30 18:57           ` Sedat Dilek
2020-05-31  1:57             ` Jens Axboe
     [not found]               ` <CA+icZUXxmOA-5+dukCgxfSp4eVHB+QaAHO6tsgq0iioQs3Af-w@mail.gmail.com>
2020-05-31  7:12                 ` Sedat Dilek
2020-06-01 13:35                   ` Sedat Dilek
2020-06-01 14:04                     ` Jens Axboe
2020-06-01 14:13                       ` Sedat Dilek
2020-06-01 14:14                         ` Jens Axboe
2020-06-01 14:35                           ` Jens Axboe
2020-06-01 14:43                             ` Sedat Dilek
2020-06-01 14:46                               ` Jens Axboe
2020-06-01 14:51                                 ` Sedat Dilek
2020-06-01 20:18                                 ` Sedat Dilek
     [not found] ` <20200604005916.niy2mejjcsx4sv6t@alap3.anarazel.de>
2020-06-04  1:04   ` Jens Axboe
2020-06-04  1:30     ` Andres Freund
2020-06-05 19:56       ` Andres Freund
2020-06-05 14:42     ` Jens Axboe
2020-06-05 20:20       ` Andres Freund
2020-06-05 20:21         ` Jens Axboe
2020-06-05 20:36         ` Andres Freund
2020-06-05 20:53           ` Jens Axboe
2020-06-05 21:13             ` Jens Axboe
2020-06-05 21:21               ` Jens Axboe
2020-06-05 22:30                 ` Andres Freund
2020-06-05 22:36                   ` Andres Freund
2020-06-05 22:49                     ` Jens Axboe
2020-06-05 22:54                       ` Andres Freund
2020-06-05 22:56                         ` Jens Axboe
2020-06-05 23:02                           ` Andres Freund
2020-06-06  0:33                 ` Sedat Dilek
2020-06-06 16:04                   ` Jens Axboe

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