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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, 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: Mon, 20 May 2019 15:45:46 -0700	[thread overview]
Message-ID: <238e14ff-68d1-3b21-a291-28de4f2d77af@csail.mit.edu> (raw)
In-Reply-To: <07D11833-8285-49C2-943D-E4C1D23E8859@linaro.org>

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)? That does give me a 20x
speedup with bs=512, but much more with a bigger block size (achieving
a max throughput of about 110 MB/s).

dd if=/dev/zero of=/dev/sdc bs=512 count=10000 conv=fsync
10000+0 records in
10000+0 records out
5120000 bytes (5.1 MB, 4.9 MiB) copied, 0.15257 s, 33.6 MB/s

dd if=/dev/zero of=/dev/sdc bs=4k count=10000 conv=fsync
10000+0 records in
10000+0 records out
40960000 bytes (41 MB, 39 MiB) copied, 0.395081 s, 104 MB/s

I'm testing this on a Toshiba MG03ACA1 (1TB) hard disk.

> Second, the commands I used follow.  Do they implement your test case
> correctly?
> 
> [root@localhost tmp]# mkdir /sys/fs/cgroup/blkio/testgrp
> [root@localhost tmp]# echo $BASHPID > /sys/fs/cgroup/blkio/testgrp/cgroup.procs
> [root@localhost tmp]# cat /sys/block/sda/queue/scheduler
> [mq-deadline] bfq none
> [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
> [root@localhost tmp]# echo bfq > /sys/block/sda/queue/scheduler
> [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, 20,1953 s, 254 kB/s
> 

Yes, this is indeed the testcase, although I see a much bigger
drop in performance with bfq, compared to the results from
your setup.

Regards,
Srivatsa

  reply	other threads:[~2019-05-20 22:45 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 [this message]
2019-05-21  6:23         ` Paolo Valente
2019-05-21  7:19           ` Srivatsa S. Bhat
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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