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From: "Srivatsa S. Bhat" <srivatsa@csail.mit.edu>
To: Paolo Valente <paolo.valente@linaro.org>
Cc: linux-fsdevel@vger.kernel.org,
	linux-block <linux-block@vger.kernel.org>,
	linux-ext4@vger.kernel.org, cgroups@vger.kernel.org,
	kernel list <linux-kernel@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
	jmoyer@redhat.com, Theodore Ts'o <tytso@mit.edu>,
	amakhalov@vmware.com, anishs@vmware.com, srivatsab@vmware.com
Subject: Re: CFQ idling kills I/O performance on ext4 with blkio cgroup controller
Date: Tue, 21 May 2019 00:19:29 -0700	[thread overview]
Message-ID: <f2141868-e882-c60d-8bb0-88d2dba53a74@csail.mit.edu> (raw)
In-Reply-To: <6EB6C9D2-E774-48FA-AC95-BC98D97645D0@linaro.org>

On 5/20/19 11:23 PM, Paolo Valente wrote:
> 
> 
>> Il giorno 21 mag 2019, alle ore 00:45, Srivatsa S. Bhat <srivatsa@csail.mit.edu> ha scritto:
>>
>> On 5/20/19 3:19 AM, Paolo Valente wrote:
>>>
>>>
>>>> Il giorno 18 mag 2019, alle ore 22:50, Srivatsa S. Bhat <srivatsa@csail.mit.edu> ha scritto:
>>>>
>>>> On 5/18/19 11:39 AM, Paolo Valente wrote:
>>>>> I've addressed these issues in my last batch of improvements for BFQ,
>>>>> which landed in the upcoming 5.2. If you give it a try, and still see
>>>>> the problem, then I'll be glad to reproduce it, and hopefully fix it
>>>>> for you.
>>>>>
>>>>
>>>> Hi Paolo,
>>>>
>>>> Thank you for looking into this!
>>>>
>>>> I just tried current mainline at commit 72cf0b07, but unfortunately
>>>> didn't see any improvement:
>>>>
>>>> dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync
>>>>
>>>> With mq-deadline, I get:
>>>>
>>>> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 3.90981 s, 1.3 MB/s
>>>>
>>>> With bfq, I get:
>>>> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 84.8216 s, 60.4 kB/s
>>>>
>>>
>>> Hi Srivatsa,
>>> thanks for reproducing this on mainline.  I seem to have reproduced a
>>> bonsai-tree version of this issue.  Before digging into the block
>>> trace, I'd like to ask you for some feedback.
>>>
>>> First, in my test, the total throughput of the disk happens to be
>>> about 20 times as high as that enjoyed by dd, regardless of the I/O
>>> scheduler.  I guess this massive overhead is normal with dsync, but
>>> I'd like know whether it is about the same on your side.  This will
>>> help me understand whether I'll actually be analyzing about the same
>>> problem as yours.
>>>
>>
>> Do you mean to say the throughput obtained by dd'ing directly to the
>> block device (bypassing the filesystem)?
> 
> No no, I mean simply what follows.
> 
> 1) in one terminal:
> [root@localhost tmp]# dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync
> 10000+0 record dentro
> 10000+0 record fuori
> 5120000 bytes (5,1 MB, 4,9 MiB) copied, 14,6892 s, 349 kB/s
> 
> 2) In a second terminal, while the dd is in progress in the first
> terminal:
> $ iostat -tmd /dev/sda 3
> Linux 5.1.0+ (localhost.localdomain) 	20/05/2019 	_x86_64_	(2 CPU)
> 
> ...
> 20/05/2019 11:40:17
> Device             tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
> sda            2288,00         0,00         9,77          0         29
> 
> 20/05/2019 11:40:20
> Device             tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
> sda            2325,33         0,00         9,93          0         29
> 
> 20/05/2019 11:40:23
> Device             tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
> sda            2351,33         0,00        10,05          0         30
> ...
> 
> As you can see, the overall throughput (~10 MB/s) is more than 20
> times as high as the dd throughput (~350 KB/s).  But the dd is the
> only source of I/O.
> 
> Do you also see such a huge difference?
> 
Ah, I see what you mean. Yes, I get a huge difference as well:

I/O scheduler    dd throughput    Total throughput (via iostat)
-------------    -------------    -----------------------------

mq-deadline
    or              1.6 MB/s               50 MB/s (30x)
  kyber

   bfq               60 KB/s                1 MB/s (16x)


Regards,
Srivatsa
VMware Photon OS

  reply	other threads:[~2019-05-21  7:19 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-17 22:16 Srivatsa S. Bhat
2019-05-18 18:39 ` Paolo Valente
2019-05-18 19:28   ` Theodore Ts'o
2019-05-20  9:15     ` Jan Kara
2019-05-20 10:45       ` Paolo Valente
2019-05-21 16:48       ` Theodore Ts'o
2019-05-21 18:19         ` Josef Bacik
2019-05-21 19:10           ` Theodore Ts'o
2019-05-20 10:38     ` Paolo Valente
2019-05-21  7:38       ` Andrea Righi
2019-05-18 20:50   ` Srivatsa S. Bhat
2019-05-20 10:19     ` Paolo Valente
2019-05-20 22:45       ` Srivatsa S. Bhat
2019-05-21  6:23         ` Paolo Valente
2019-05-21  7:19           ` Srivatsa S. Bhat [this message]
2019-05-21  9:10           ` Jan Kara
2019-05-21 16:31             ` Theodore Ts'o
2019-05-21 11:25       ` Paolo Valente
2019-05-21 13:20         ` Paolo Valente
2019-05-21 16:21           ` Paolo Valente
2019-05-21 17:38             ` Paolo Valente
2019-05-21 22:51               ` Srivatsa S. Bhat
2019-05-22  8:05                 ` Paolo Valente
2019-05-22  9:02                   ` Srivatsa S. Bhat
2019-05-22  9:12                     ` Paolo Valente
2019-05-22 10:02                       ` Srivatsa S. Bhat
2019-05-22  9:09                   ` Paolo Valente
2019-05-22 10:01                     ` Srivatsa S. Bhat
2019-05-22 10:54                       ` Paolo Valente
2019-05-23  2:30                         ` Srivatsa S. Bhat
2019-05-23  9:19                           ` Paolo Valente
2019-05-23 17:22                             ` Paolo Valente
2019-05-23 23:43                               ` Srivatsa S. Bhat
2019-05-24  6:51                                 ` Paolo Valente
2019-05-24  7:56                                   ` Paolo Valente
2019-05-29  1:09                                   ` Srivatsa S. Bhat
2019-05-29  7:41                                     ` Paolo Valente
2019-05-30  8:29                                       ` Srivatsa S. Bhat
2019-05-30 10:45                                         ` Paolo Valente
2019-06-02  7:04                                           ` Srivatsa S. Bhat
2019-06-11 22:34                                             ` Srivatsa S. Bhat
2019-06-12 13:04                                               ` Jan Kara
2019-06-12 19:36                                                 ` Srivatsa S. Bhat
2019-06-13  6:02                                                   ` Greg Kroah-Hartman
2019-06-13 19:03                                                     ` Srivatsa S. Bhat
2019-06-13  8:20                                                   ` Jan Kara
2019-06-13 19:05                                                     ` Srivatsa S. Bhat
2019-06-13  8:37                                                   ` Jens Axboe
2019-06-13  5:46                                               ` Paolo Valente
2019-06-13 19:13                                                 ` Srivatsa S. Bhat
2019-05-23 23:32                           ` Srivatsa S. Bhat
2019-05-30  8:38                             ` Srivatsa S. Bhat

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