General question (scheduler) with SSDs?

General question (scheduler) with SSDs?

[Justin Piszcz]

Hello,

I was curious if anyone had done any benchmarks and/or has conclusive 
information, what is the best Linux scheduler to use with SSDs?

Noop?
CFQ?
AS?
Deadline?

Justin.

Re: General question (scheduler) with SSDs?

[Pádraig Brady]

Justin Piszcz wrote:
> Hello,
> 
> I was curious if anyone had done any benchmarks and/or has conclusive
> information, what is the best Linux scheduler to use with SSDs?
> 
> Noop?
> CFQ?
> AS?
> Deadline?

There was a thread started on that recently:
http://lkml.org/lkml/2009/1/30/288

Re: General question (scheduler) with SSDs?

[Sitsofe Wheeler]

On Thu, Feb 19, 2009 at 08:38:38AM -0500, Justin Piszcz wrote:
> Hello,
> 
> I was curious if anyone had done any benchmarks and/or has conclusive 
> information, what is the best Linux scheduler to use with SSDs?
> 
> Noop?
> CFQ?
> AS?
> Deadline?

As mentioned in another mail :wq


-- 
Sitsofe | http://sucs.org/~sits/

Re: General question (scheduler) with SSDs?

[Sitsofe Wheeler]

Whoops, I didn't mean to send that previous half formed mail :) Sorry.

On Thu, Feb 19, 2009 at 08:38:38AM -0500, Justin Piszcz wrote:
> 
> I was curious if anyone had done any benchmarks and/or has conclusive 
> information, what is the best Linux scheduler to use with SSDs?
> 
> Noop?
> CFQ?
> AS?
> Deadline?

As mentioned in another mail there was a discussion on
http://lkml.org/lkml/2009/1/31/28 and long thread talking about the
introduction of the rotational flag here
http://lkml.org/lkml/2009/1/5/340 . Cheapo SSDs or even USB keys are not
auto detected as non-rotational devices by the kernel and after a bit of
poking about I've come up with the following udev rules for my
particular cases:

SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{model}=="ASUS-PHISON *", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{idVendor}=="0951", ATTRS{idProduct}=="1606", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{manufacturer}=="SanDisk", ATTRS{product}=="Cruzer Micro", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"

Ever since the rotational option appeared I've been trying cfq but prior
to that I was using noop or deadline. However it doesn't look like
anyone has sat down and run the numbers to see what affect the
ioscheulder/rotational flag is having on cheapo SSDs - all the
suggestions are anecdotal. Could you run some benchmarks with these
different options and report back the results?

-- 
Sitsofe | http://sucs.org/~sits/

Re: General question (scheduler) with SSDs?

[Justin Piszcz]

On Fri, 20 Feb 2009, Sitsofe Wheeler wrote:

> Whoops, I didn't mean to send that previous half formed mail :) Sorry.
>
> As mentioned in another mail there was a discussion on
> http://lkml.org/lkml/2009/1/31/28 and long thread talking about the
> introduction of the rotational flag here
> http://lkml.org/lkml/2009/1/5/340 . Cheapo SSDs or even USB keys are not
> auto detected as non-rotational devices by the kernel and after a bit of
> poking about I've come up with the following udev rules for my
> particular cases:
>
> SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{model}=="ASUS-PHISON *", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
> SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{idVendor}=="0951", ATTRS{idProduct}=="1606", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
> SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{manufacturer}=="SanDisk", ATTRS{product}=="Cruzer Micro", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
>
> Ever since the rotational option appeared I've been trying cfq but prior
> to that I was using noop or deadline. However it doesn't look like
> anyone has sat down and run the numbers to see what affect the
> ioscheulder/rotational flag is having on cheapo SSDs - all the
> suggestions are anecdotal. Could you run some benchmarks with these
> different options and report back the results?
>
> -- 
> Sitsofe | http://sucs.org/~sits/
>

$ grep rotational -r /usr/src/linux/
/usr/src/linux/drivers/scsi/NCR5380.c: * USLEEP_POLL should be a maximum rotational latency.
/usr/src/linux/fs/partitions/sun.c:             __be16 rspeed;     /* Disk rotational speed */
/usr/src/linux/fs/ufs/ufs_fs.h: * Compute the cylinder and rotational position of a cyl block addr.
/usr/src/linux/fs/ufs/ufs_fs.h: __fs32  fs_nrpos;               /* number of rotational positions */
/usr/src/linux/fs/ufs/ufs_fs.h:#define UFS_42POSTBLFMT          -1      /* 4.2BSD rotational table format */
/usr/src/linux/fs/ufs/ufs_fs.h:#define UFS_DYNAMICPOSTBLFMT     1       /* dynamic rotational table format */
/usr/src/linux/fs/ufs/ufs_fs.h: __s32   s_nrpos;        /* number of rotational positions */
/usr/src/linux/include/linux/blkdev.h:#define QUEUE_FLAG_NONROT      14 /* non-rotational device (SSD) */
/usr/src/linux/include/linux/genhd.h:   __u16   d_rpm;                  /* rotational speed */

# find /sys/|grep -i rotational
#

Which kernel{option} do you enable to enable support for that option in /sys?

Justin.

Re: General question (scheduler) with SSDs?

[Sitsofe Wheeler]

On Fri, Feb 20, 2009 at 05:37:44AM -0500, Justin Piszcz wrote:
> 
> Which kernel{option} do you enable to enable support for that option in 
> /sys?

It's new to 2.6.29 (it's available in at least 2.6.29rc5). I don't
believe I enabled anything special to get it.

-- 
Sitsofe | http://sucs.org/~sits/

Re: General question (scheduler) with SSDs?

[Kay Sievers]

On Fri, Feb 20, 2009 at 10:43, Sitsofe Wheeler <sitsofe@yahoo.com> wrote:
> Whoops, I didn't mean to send that previous half formed mail :) Sorry.
>
> On Thu, Feb 19, 2009 at 08:38:38AM -0500, Justin Piszcz wrote:
>>
>> I was curious if anyone had done any benchmarks and/or has conclusive
>> information, what is the best Linux scheduler to use with SSDs?
>>
>> Noop?
>> CFQ?
>> AS?
>> Deadline?
>
> As mentioned in another mail there was a discussion on
> http://lkml.org/lkml/2009/1/31/28 and long thread talking about the
> introduction of the rotational flag here
> http://lkml.org/lkml/2009/1/5/340 . Cheapo SSDs or even USB keys are not
> auto detected as non-rotational devices by the kernel and after a bit of
> poking about I've come up with the following udev rules for my
> particular cases:
>
> SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{model}=="ASUS-PHISON *", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"

Udev can write to the attribute itself. This should be all you need:
  SUSBSYTEM=="block", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="1"

Kay

Re: General question (scheduler) with SSDs?

[Sitsofe Wheeler]

On Fri, Feb 20, 2009 at 12:16:42PM +0100, Kay Sievers wrote:
> 
> Udev can write to the attribute itself. This should be all you need:
>   SUSBSYTEM=="block", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="1"

I tried 
SUBSYSTEM=="block", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="0"
but udevtest /sys/block/sda/ doesn't list it as firing (udev 117-8)...

-- 
Sitsofe | http://sucs.org/~sits/

Re: General question (scheduler) with SSDs?

[Kay Sievers]

On Fri, Feb 20, 2009 at 14:12, Sitsofe Wheeler <sitsofe@yahoo.com> wrote:
> On Fri, Feb 20, 2009 at 12:16:42PM +0100, Kay Sievers wrote:
>>
>> Udev can write to the attribute itself. This should be all you need:
>>   SUSBSYTEM=="block", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="1"
>
> I tried
> SUBSYSTEM=="block", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="0"
> but udevtest /sys/block/sda/ doesn't list it as firing (udev 117-8)...

I does here:
  udev_rules_apply_to_event: ATTR '/sys/devices/ ...
/sdb/queue/rotational' writing '0'

  $grep . /sys/class/block/*/queue/rotational
  /sys/class/block/sda/queue/rotational:1
  /sys/class/block/sdb/queue/rotational:0

Maybe "udevtest" is not showing it for you, or udev 117 is too old and
does not work that way.

Thanks,
Kay

Re: General question (scheduler) with SSDs?

[Sitsofe Wheeler]

On Fri, Feb 20, 2009 at 02:23:38PM +0100, Kay Sievers wrote:
> On Fri, Feb 20, 2009 at 14:12, Sitsofe Wheeler <sitsofe@yahoo.com> wrote:
> >
> > I tried
> > SUBSYSTEM=="block", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="0"
> > but udevtest /sys/block/sda/ doesn't list it as firing (udev 117-8)...
> 
> I does here:
>   udev_rules_apply_to_event: ATTR '/sys/devices/ ...
> /sdb/queue/rotational' writing '0'
> 
>   $grep . /sys/class/block/*/queue/rotational
>   /sys/class/block/sda/queue/rotational:1
>   /sys/class/block/sdb/queue/rotational:0
> 
> Maybe "udevtest" is not showing it for you, or udev 117 is too old and
> does not work that way.

After you mentioned this I tried again and seemingly I was mistaken - it
does work as you described. I had to make a slight rule tweak to stop
it matching on partitions though:

SUBSYSTEM=="block", KERNEL=="[sh]d[a-z]", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="0"
SUBSYSTEM=="block", KERNEL=="[sh]d[a-z]", ATTRS{idVendor}=="0951", ATTRS{idProduct}=="1606", ATTR{queue/rotational}="0"
SUBSYSTEM=="block", KERNEL=="[sh]d[a-z]", ATTRS{manufacturer}=="SanDisk", ATTRS{product}=="Cruzer Micro", ATTR{queue/rotational}="0"

Thanks!

-- 
Sitsofe | http://sucs.org/~sits/

Re: General question (scheduler) with SSDs?

[Kay Sievers]

On Fri, Feb 20, 2009 at 15:27, Sitsofe Wheeler <sitsofe@yahoo.com> wrote:
> On Fri, Feb 20, 2009 at 02:23:38PM +0100, Kay Sievers wrote:
>> On Fri, Feb 20, 2009 at 14:12, Sitsofe Wheeler <sitsofe@yahoo.com> wrote:
>> >
>> > I tried
>> > SUBSYSTEM=="block", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="0"
>> > but udevtest /sys/block/sda/ doesn't list it as firing (udev 117-8)...
>>
>> I does here:
>>   udev_rules_apply_to_event: ATTR '/sys/devices/ ...
>> /sdb/queue/rotational' writing '0'
>>
>>   $grep . /sys/class/block/*/queue/rotational
>>   /sys/class/block/sda/queue/rotational:1
>>   /sys/class/block/sdb/queue/rotational:0
>>
>> Maybe "udevtest" is not showing it for you, or udev 117 is too old and
>> does not work that way.
>
> After you mentioned this I tried again and seemingly I was mistaken - it
> does work as you described.

Great.

> I had to make a slight rule tweak to stop
> it matching on partitions though:
>
> SUBSYSTEM=="block", KERNEL=="[sh]d[a-z]", ATTRS{model}=="ASUS-PHISON *", ATTR{queue/rotational}="0"

Newer kernels have DEVTYPE in the envent environment, and:
  ENV{DEVTYPE}=="disk"
can be used, which is easier and more reliable.

Also the whitespace after "...PHISON *" does not need to be matched.
If the match value does not end in whitespace itself, udev will match
against the value with all trailing whitespace ignored.

Kay

Re: General question (scheduler) with SSDs?

[Sitsofe Wheeler]

On Fri, Feb 20, 2009 at 03:56:06PM +0100, Kay Sievers wrote:
> Also the whitespace after "...PHISON *" does not need to be matched.
> If the match value does not end in whitespace itself, udev will match
> against the value with all trailing whitespace ignored.

Ah, I'm not matching against only whitespace:

$ cat /sys/block/*/device/model 
ASUS-PHISON OB S
ASUS-PHISON SSD 

(the first is the builtin faster SSD, the other is the slower removable
SSD).

-- 
Sitsofe | http://sucs.org/~sits/

Re: General question (scheduler) with SSDs?

[Kay Sievers]

On Fri, Feb 20, 2009 at 20:25, Sitsofe Wheeler <sitsofe@yahoo.com> wrote:
> On Fri, Feb 20, 2009 at 03:56:06PM +0100, Kay Sievers wrote:
>> Also the whitespace after "...PHISON *" does not need to be matched.
>> If the match value does not end in whitespace itself, udev will match
>> against the value with all trailing whitespace ignored.
>
> Ah, I'm not matching against only whitespace:
>
> $ cat /sys/block/*/device/model
> ASUS-PHISON OB S
> ASUS-PHISON SSD
>
> (the first is the builtin faster SSD, the other is the slower removable
> SSD).

Ah, I see, then nothing to complain from my side anymore. :)

Thanks,
Kay