linux-kernel - Re: fio rand read/write regression with 2.6.32-rc3

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Date:	Mon, 12 Oct 2009 13:50:16 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: fio rand read/write regression with 2.6.32-rc3

On Sun, 2009-10-11 at 10:23 +0200, Corrado Zoccolo wrote:
> On Sat, Oct 10, 2009 at 11:52 AM, Zhang, Yanmin
> <yanmin_zhang@...ux.intel.com> wrote:
> > On Sat, 2009-10-10 at 10:01 +0200, Jens Axboe wrote:
> >> On Sat, Oct 10 2009, Zhang, Yanmin wrote:
> >> > Comparing with 2.6.23-rc1's result, fio rand read write has regression
> >> > on my 2*4 core stoakley machine (8GB memory) with a JBOD of 12 disks.
> >> >
> >> > Every disk has 8 1-GB files. Start 8 sub-processes per disk and every
> >> > process random chooses a file on the disk to do 36 times of file read or
> >> > write on the file and then choose another file.
> >> >
> >> >
> >> > fio_mmap_rand_read_4k regresion is about 35%.
> >>
> >> Heh, I seem to recollect I told Linus that this would cost is 30-40%
> >> performance. So not totally crazy.
> >>
> >> So yes, this isn't hugely unexpected. If you send me your fio job files,
> >> I'll try and see what I can do about it.
> > See the attachment.
> >
> Hi Yanmin,
> the fio test you sent just performs random read, no write seems involved here.

Sorry for not sending all the job files because they are similiar and big.
You could change the job file to run rand write and readwrite.

> I suspect that you should be able to observe the same regression if
> you just run on a single disk. Can you confirm?
> Is your disk a SATA2 rotational disk with NCQ?
It's a JOBD with 12 SAS disks.

Another machine's JBOD has 13 SCSI disks.

Based on your suggestion, I tested it on a single SAS disk (create 8 1-GB file and
start 8 processes) and get 30% regression. On a single SCSI disk, there is also about
30% regression. On a single SATA (SATA link up 1.5 Gbps) disk with NCQ, the regression
is about 20%.

Perhaps the job file causes fio to deliver too many I/O requests, sometimes kernel
print out some blocking info like below:

Apr  8 23:54:19 lkp-tulsa01-x8664 kernel: INFO: task kjournald:6261 blocked for more than 120 seconds.
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel: kjournald     D ffff88002f228180     0  6261      2
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel:  ffff88027ab09910 0000000000000046 0000000000000000 ffff88027cc20440
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel:  ffff88027f0c66a0 ffff88027ab09bb0 0000000100000e56 000000007cc20440
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel:  ffff88027a915480 ffffffff803678a9 0000000000000000 0000000100000000
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel: Call Trace:
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel:  [<ffffffff803678a9>] ? __make_request+0x310/0x40b
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel:  [<ffffffff802b5571>] ? sync_buffer+0x0/0x3f
Apr  8 23:54:19 lkp-tulsa01-x8664 kernel:  [<ffffffff805aeadf>] ? schedule+0x9/0x1d


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