scheduler question 2.6.16.x

scheduler question 2.6.16.x

[Nick Warne]

Hi all,

I see in menuconfig I have two options:

<*> Anticipatory I/O scheduler
<*> Deadline I/O scheduler

Help reveals Anticipatory is pretty good, but make a slightly larger kernel - 
Deadline help says it a good alternative to Anticipatory.

But I can build both in... so I guess then the kernel decides what is the best 
to use?  Or should it be so I am only allowed to select one or the other and 
allowing both is an oversight?

Thanks,

Nick
-- 
"Person who say it cannot be done should not interrupt person doing it."
-Chinese Proverb

Re: scheduler question 2.6.16.x

[Jens Axboe]

On Tue, Apr 25 2006, Nick Warne wrote:
> Hi all,
> 
> I see in menuconfig I have two options:
> 
> <*> Anticipatory I/O scheduler
> <*> Deadline I/O scheduler
> 
> Help reveals Anticipatory is pretty good, but make a slightly larger
> kernel - Deadline help says it a good alternative to Anticipatory.
> 
> But I can build both in... so I guess then the kernel decides what is
> the best to use?  Or should it be so I am only allowed to select one
> or the other and allowing both is an oversight?

See the option no more than two lines down from that, default io
scheduler. Also see Documentation/block/switching-sched.txt and/or
Documentation/kernel-parameters.txt (elevator=) section.

-- 
Jens Axboe

Re: scheduler question 2.6.16.x

[Nick Warne]

On Tuesday 25 April 2006 19:15, Jens Axboe wrote:

> > But I can build both in... so I guess then the kernel decides what is
> > the best to use?  Or should it be so I am only allowed to select one
> > or the other and allowing both is an oversight?
>
> See the option no more than two lines down from that, default io
> scheduler. Also see Documentation/block/switching-sched.txt and/or
> Documentation/kernel-parameters.txt (elevator=) section.

Hi Jens,

I haven't got the switching-sched.txt, although I found a sched-design.txt... 
but what I meant was if I select whatever default, do/can I still need to 
select either/or scheduler?

i.e. why doesn't 'default selection option' only allow that scheduler to be 
selected?

Nick
-- 
"Person who say it cannot be done should not interrupt person doing it."
-Chinese Proverb

Re: scheduler question 2.6.16.x

[Jens Axboe]

On Tue, Apr 25 2006, Nick Warne wrote:
> On Tuesday 25 April 2006 19:15, Jens Axboe wrote:
> 
> > > But I can build both in... so I guess then the kernel decides what is
> > > the best to use?  Or should it be so I am only allowed to select one
> > > or the other and allowing both is an oversight?
> >
> > See the option no more than two lines down from that, default io
> > scheduler. Also see Documentation/block/switching-sched.txt and/or
> > Documentation/kernel-parameters.txt (elevator=) section.
> 
> Hi Jens,
> 
> I haven't got the switching-sched.txt, although I found a
> sched-design.txt...  but what I meant was if I select whatever
> default, do/can I still need to select either/or scheduler?
> 
> i.e. why doesn't 'default selection option' only allow that scheduler
> to be selected?

I don't understand your question, but here's how it works. You can
select as many/few schedulers as you want. You can only set a scheduler
default, if it's compiled in (y, not m). If you don't select any
schedulers, noop is still selected and wil be the default.

Just try the options, you'll see how they work...

-- 
Jens Axboe

Re: scheduler question 2.6.16.x

[Andre Tomt]

Nick Warne wrote:
> On Tuesday 25 April 2006 19:15, Jens Axboe wrote:
> 
>>> But I can build both in... so I guess then the kernel decides what is
>>> the best to use?  Or should it be so I am only allowed to select one
>>> or the other and allowing both is an oversight?
>> See the option no more than two lines down from that, default io
>> scheduler. Also see Documentation/block/switching-sched.txt and/or
>> Documentation/kernel-parameters.txt (elevator=) section.
> 
> Hi Jens,
> 
> I haven't got the switching-sched.txt, although I found a sched-design.txt... 
> but what I meant was if I select whatever default, do/can I still need to 
> select either/or scheduler?
> 
> i.e. why doesn't 'default selection option' only allow that scheduler to be 
> selected?

That would be a artificial (and silly!) limit - the io-scheduler is 
pluggable and selectable at boot, you can even change it at run time at 
a per block device level.

See the elevator= boot option and /sys/block/<device>/queue/scheduler

Re: scheduler question 2.6.16.x

[Nick Warne]

On Wednesday 26 April 2006 19:09, Andre Tomt wrote:

> > i.e. why doesn't 'default selection option' only allow that scheduler to
> > be selected?
>
> That would be a artificial (and silly!) limit - the io-scheduler is
> pluggable and selectable at boot, you can even change it at run time at
> a per block device level.
>
> See the elevator= boot option and /sys/block/<device>/queue/scheduler

Ohh!  I see.  That is what I was sort of asking (but didn't know what 
precisely to ask)... OK thanks, understand now.

Nick


-- 
"Person who say it cannot be done should not interrupt person doing it."
-Chinese Proverb

Re: scheduler question 2.6.16.x

[Bill Davidsen]

Nick Warne wrote:
> On Tuesday 25 April 2006 19:15, Jens Axboe wrote:
> 
>>> But I can build both in... so I guess then the kernel decides what is
>>> the best to use?  Or should it be so I am only allowed to select one
>>> or the other and allowing both is an oversight?
>> See the option no more than two lines down from that, default io
>> scheduler. Also see Documentation/block/switching-sched.txt and/or
>> Documentation/kernel-parameters.txt (elevator=) section.
> 
> Hi Jens,
> 
> I haven't got the switching-sched.txt, although I found a sched-design.txt... 
> but what I meant was if I select whatever default, do/can I still need to 
> select either/or scheduler?
> 
> i.e. why doesn't 'default selection option' only allow that scheduler to be 
> selected?

Not clear is you mean "allow that to the the only selection" which it 
does, or "only allow that selection" which makes no sense, you can boot 
using any compiled scheduler.

My configuration for beverage is set to "cask conditioned IPA" but I 
have most of the "Microbrewed" selections for IPA, PA, Stout and Porter 
compiled in. The "bland American and imported brews" section is 
disabled, with "water" enabled as a module.

The preference is what you use by default, but not an irrevocable choice.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me