diff mbox

[v3,2/5] build: Hook the schedulers into Kconfig

Message ID 1452187761-38328-3-git-send-email-jonathan.creekmore@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Jonathan Creekmore Jan. 7, 2016, 5:29 p.m. UTC
Allow the schedulers to be independently enabled or disabled at
compile-time. To match existing behavior, all four schedulers are
compiled in by default, although the Credit2, RTDS, and ARINC653 are
marked EXPERIMENTAL to match their not currently supported status.

CC: George Dunlap <george.dunlap@eu.citrix.com>
CC: Dario Faggioli <dario.faggioli@citrix.com>
Signed-off-by: Jonathan Creekmore <jonathan.creekmore@gmail.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>

---
Changed since v2:

  * Hid the scheduler menu behind the EXPERT option
  * Provide static inlines for credit functions that are assumed to be
    always available
  * Provide an absolute default of the credit scheduler if the
    scheduler menu is not visible

Changed since v1:

  * Marked credit2 as EXPERIMENTAL
  * Removed confusing language from the commit message
  * Alphabetize the schedulers
---
 xen/common/Kconfig      | 67 +++++++++++++++++++++++++++++++++++++++++++++++++
 xen/common/Makefile     |  8 +++---
 xen/common/schedule.c   | 12 +++++++--
 xen/include/xen/sched.h |  5 ++++
 4 files changed, 86 insertions(+), 6 deletions(-)

Comments

Konrad Rzeszutek Wilk Jan. 8, 2016, 3:47 p.m. UTC | #1
On Thu, Jan 07, 2016 at 11:29:18AM -0600, Jonathan Creekmore wrote:
> Allow the schedulers to be independently enabled or disabled at
> compile-time. To match existing behavior, all four schedulers are
> compiled in by default, although the Credit2, RTDS, and ARINC653 are
> marked EXPERIMENTAL to match their not currently supported status.

By unmarking all of them in sequence I was able to get this:

#
# Schedulers
#
# CONFIG_SCHED_CREDIT is not set
# CONFIG_SCHED_CREDIT2 is not set
# CONFIG_SCHED_RTDS is not set
# CONFIG_SCHED_ARINC653 is not set
# CONFIG_SCHED_CREDIT_DEFAULT is not set
# CONFIG_SCHED_CREDIT2_DEFAULT is not set
# CONFIG_SCHED_RTDS_DEFAULT is not set
# CONFIG_SCHED_ARINC653_DEFAULT is not set
CONFIG_SCHED_DEFAULT="credit"


And the hypervisor did build with:

[konrad@char xen]$ nm --defined xen-syms |grep schedulers
ffff82d080290d58 D __end_schedulers_array
ffff82d080290d58 D __start_schedulers_array

:-)

Not exactly sure if there is some way to make us _not_ shoot
ourselves in the foot by mistake.

Perhaps the build should complain if the size of the
__schedulers_array is zero?
Andrew Cooper Jan. 8, 2016, 3:54 p.m. UTC | #2
On 08/01/16 15:47, Konrad Rzeszutek Wilk wrote:
> On Thu, Jan 07, 2016 at 11:29:18AM -0600, Jonathan Creekmore wrote:
>> Allow the schedulers to be independently enabled or disabled at
>> compile-time. To match existing behavior, all four schedulers are
>> compiled in by default, although the Credit2, RTDS, and ARINC653 are
>> marked EXPERIMENTAL to match their not currently supported status.
> By unmarking all of them in sequence I was able to get this:
>
> #
> # Schedulers
> #
> # CONFIG_SCHED_CREDIT is not set
> # CONFIG_SCHED_CREDIT2 is not set
> # CONFIG_SCHED_RTDS is not set
> # CONFIG_SCHED_ARINC653 is not set
> # CONFIG_SCHED_CREDIT_DEFAULT is not set
> # CONFIG_SCHED_CREDIT2_DEFAULT is not set
> # CONFIG_SCHED_RTDS_DEFAULT is not set
> # CONFIG_SCHED_ARINC653_DEFAULT is not set
> CONFIG_SCHED_DEFAULT="credit"
>
>
> And the hypervisor did build with:
>
> [konrad@char xen]$ nm --defined xen-syms |grep schedulers
> ffff82d080290d58 D __end_schedulers_array
> ffff82d080290d58 D __start_schedulers_array
>
> :-)
>
> Not exactly sure if there is some way to make us _not_ shoot
> ourselves in the foot by mistake.
>
> Perhaps the build should complain if the size of the
> __schedulers_array is zero?

Hmm yes - an ASSERT() at the bottom of the linker file would be a very
good defensive measure.

A hypervisor without any schedulers compiled in will be rather sad.

~Andrew
Dario Faggioli Jan. 8, 2016, 3:59 p.m. UTC | #3
On Fri, 2016-01-08 at 15:54 +0000, Andrew Cooper wrote:
> On 08/01/16 15:47, Konrad Rzeszutek Wilk wrote:
> > 
> > And the hypervisor did build with:
> > 
> > [konrad@char xen]$ nm --defined xen-syms |grep schedulers
> > ffff82d080290d58 D __end_schedulers_array
> > ffff82d080290d58 D __start_schedulers_array
> > 
> > :-)
> > 
> > Not exactly sure if there is some way to make us _not_ shoot
> > ourselves in the foot by mistake.
> > 
> > Perhaps the build should complain if the size of the
> > __schedulers_array is zero?
> 
> Hmm yes - an ASSERT() at the bottom of the linker file would be a
> very
> good defensive measure.
> 
+1

> A hypervisor without any schedulers compiled in will be rather sad.
> 
Well, it depends on how many pCPUs the host you want to run the
hypervisor on has: if it has 0 of them, no scheduler at all is the
perfect solution... not to mention that the combination of these things
(0 CPUs and no scheduling), would make a lot of issues just instantly
disappear! :-D

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
Jonathan Creekmore Jan. 8, 2016, 4:02 p.m. UTC | #4
Andrew Cooper writes:

> On 08/01/16 15:47, Konrad Rzeszutek Wilk wrote:
>> On Thu, Jan 07, 2016 at 11:29:18AM -0600, Jonathan Creekmore wrote:
>>> Allow the schedulers to be independently enabled or disabled at
>>> compile-time. To match existing behavior, all four schedulers are
>>> compiled in by default, although the Credit2, RTDS, and ARINC653 are
>>> marked EXPERIMENTAL to match their not currently supported status.
>> By unmarking all of them in sequence I was able to get this:
>>
>> #
>> # Schedulers
>> #
>> # CONFIG_SCHED_CREDIT is not set
>> # CONFIG_SCHED_CREDIT2 is not set
>> # CONFIG_SCHED_RTDS is not set
>> # CONFIG_SCHED_ARINC653 is not set
>> # CONFIG_SCHED_CREDIT_DEFAULT is not set
>> # CONFIG_SCHED_CREDIT2_DEFAULT is not set
>> # CONFIG_SCHED_RTDS_DEFAULT is not set
>> # CONFIG_SCHED_ARINC653_DEFAULT is not set
>> CONFIG_SCHED_DEFAULT="credit"
>>
>>
>> And the hypervisor did build with:
>>
>> [konrad@char xen]$ nm --defined xen-syms |grep schedulers
>> ffff82d080290d58 D __end_schedulers_array
>> ffff82d080290d58 D __start_schedulers_array
>>
>> :-)
>>
>> Not exactly sure if there is some way to make us _not_ shoot
>> ourselves in the foot by mistake.
>>
>> Perhaps the build should complain if the size of the
>> __schedulers_array is zero?
>
> Hmm yes - an ASSERT() at the bottom of the linker file would be a very
> good defensive measure.
>
> A hypervisor without any schedulers compiled in will be rather sad.

I can definitely add that in.
Juergen Gross Jan. 8, 2016, 4:13 p.m. UTC | #5
On 08/01/16 17:02, Jonathan Creekmore wrote:
> 
> Andrew Cooper writes:
> 
>> On 08/01/16 15:47, Konrad Rzeszutek Wilk wrote:
>>> On Thu, Jan 07, 2016 at 11:29:18AM -0600, Jonathan Creekmore wrote:
>>>> Allow the schedulers to be independently enabled or disabled at
>>>> compile-time. To match existing behavior, all four schedulers are
>>>> compiled in by default, although the Credit2, RTDS, and ARINC653 are
>>>> marked EXPERIMENTAL to match their not currently supported status.
>>> By unmarking all of them in sequence I was able to get this:
>>>
>>> #
>>> # Schedulers
>>> #
>>> # CONFIG_SCHED_CREDIT is not set
>>> # CONFIG_SCHED_CREDIT2 is not set
>>> # CONFIG_SCHED_RTDS is not set
>>> # CONFIG_SCHED_ARINC653 is not set
>>> # CONFIG_SCHED_CREDIT_DEFAULT is not set
>>> # CONFIG_SCHED_CREDIT2_DEFAULT is not set
>>> # CONFIG_SCHED_RTDS_DEFAULT is not set
>>> # CONFIG_SCHED_ARINC653_DEFAULT is not set
>>> CONFIG_SCHED_DEFAULT="credit"
>>>
>>>
>>> And the hypervisor did build with:
>>>
>>> [konrad@char xen]$ nm --defined xen-syms |grep schedulers
>>> ffff82d080290d58 D __end_schedulers_array
>>> ffff82d080290d58 D __start_schedulers_array
>>>
>>> :-)
>>>
>>> Not exactly sure if there is some way to make us _not_ shoot
>>> ourselves in the foot by mistake.
>>>
>>> Perhaps the build should complain if the size of the
>>> __schedulers_array is zero?
>>
>> Hmm yes - an ASSERT() at the bottom of the linker file would be a very
>> good defensive measure.
>>
>> A hypervisor without any schedulers compiled in will be rather sad.
> 
> I can definitely add that in.

I think there should be an ASSERT (or some other measure) to
ensure the default scheduler is available.


Juergen
Jonathan Creekmore Jan. 8, 2016, 4:30 p.m. UTC | #6
Juergen Gross writes:

> On 08/01/16 17:02, Jonathan Creekmore wrote:
>>
>> Andrew Cooper writes:
>>
>>> On 08/01/16 15:47, Konrad Rzeszutek Wilk wrote:
>>>> On Thu, Jan 07, 2016 at 11:29:18AM -0600, Jonathan Creekmore wrote:
>>>>> Allow the schedulers to be independently enabled or disabled at
>>>>> compile-time. To match existing behavior, all four schedulers are
>>>>> compiled in by default, although the Credit2, RTDS, and ARINC653 are
>>>>> marked EXPERIMENTAL to match their not currently supported status.
>>>> By unmarking all of them in sequence I was able to get this:
>>>>
>>>> #
>>>> # Schedulers
>>>> #
>>>> # CONFIG_SCHED_CREDIT is not set
>>>> # CONFIG_SCHED_CREDIT2 is not set
>>>> # CONFIG_SCHED_RTDS is not set
>>>> # CONFIG_SCHED_ARINC653 is not set
>>>> # CONFIG_SCHED_CREDIT_DEFAULT is not set
>>>> # CONFIG_SCHED_CREDIT2_DEFAULT is not set
>>>> # CONFIG_SCHED_RTDS_DEFAULT is not set
>>>> # CONFIG_SCHED_ARINC653_DEFAULT is not set
>>>> CONFIG_SCHED_DEFAULT="credit"
>>>>
>>>>
>>>> And the hypervisor did build with:
>>>>
>>>> [konrad@char xen]$ nm --defined xen-syms |grep schedulers
>>>> ffff82d080290d58 D __end_schedulers_array
>>>> ffff82d080290d58 D __start_schedulers_array
>>>>
>>>> :-)
>>>>
>>>> Not exactly sure if there is some way to make us _not_ shoot
>>>> ourselves in the foot by mistake.
>>>>
>>>> Perhaps the build should complain if the size of the
>>>> __schedulers_array is zero?
>>>
>>> Hmm yes - an ASSERT() at the bottom of the linker file would be a very
>>> good defensive measure.
>>>
>>> A hypervisor without any schedulers compiled in will be rather sad.
>>
>> I can definitely add that in.
>
> I think there should be an ASSERT (or some other measure) to
> ensure the default scheduler is available.

So, in a normal configuration case, that should not be able to
happen. The way the Kconfig is set up, the default will only give you an
option to choose schedulers that are enabled in the build.

1) "normal" (non-expert) configuration --- the user never sees that
schedulers are available for configuration, so all of them are compiled
in and the credit scheduler is chosen by the default.

2) "expert" configuration --- the user can select which schedulers are
available in the build and can choose which one is the default. If a
scheduler is not selected to be part of the build, it is not available
in the default selection dialog.

3) "pathological" configuration --- the user disabled all of the
schedulers, but due to a quirk with hiding the scheduler menu for the
non-expert case, it fell back to the "credit" scheduler for the
default.

So, based on the Kconfig setup and the linker ASSERT, there should be no
way to have a default scheduler that is not in the build. I wish Kconfig
allowed you to state that you must have at least one option selected or
up to all of the options selected (so I could require 1-4 schedulers
compiled in, but not 0). Unfortunately, the only way that seems allowed
is if you compile code in as modules, which Xen does not (with a choice
block, you can select multiple items as M, but only 1 as Y, but at least
1 must be present --- since we only support Y, the choice block wouldn't
work for the schedulers).
Jan Beulich Jan. 8, 2016, 4:30 p.m. UTC | #7
>>> On 08.01.16 at 17:13, <JGross@suse.com> wrote:
> I think there should be an ASSERT (or some other measure) to
> ensure the default scheduler is available.

Indeed I was about to say exactly this.

Jan
Jan Beulich Jan. 8, 2016, 4:49 p.m. UTC | #8
>>> On 08.01.16 at 17:30, <jonathan.creekmore@gmail.com> wrote:
> So, based on the Kconfig setup and the linker ASSERT, there should be no
> way to have a default scheduler that is not in the build. I wish Kconfig
> allowed you to state that you must have at least one option selected or
> up to all of the options selected (so I could require 1-4 schedulers
> compiled in, but not 0). Unfortunately, the only way that seems allowed
> is if you compile code in as modules, which Xen does not (with a choice
> block, you can select multiple items as M, but only 1 as Y, but at least
> 1 must be present --- since we only support Y, the choice block wouldn't
> work for the schedulers).

Perhaps credit should just not be configurable then?

Jan
Doug Goldstein Jan. 8, 2016, 4:58 p.m. UTC | #9
On 1/8/16 10:49 AM, Jan Beulich wrote:
>>>> On 08.01.16 at 17:30, <jonathan.creekmore@gmail.com> wrote:
>> So, based on the Kconfig setup and the linker ASSERT, there should be no
>> way to have a default scheduler that is not in the build. I wish Kconfig
>> allowed you to state that you must have at least one option selected or
>> up to all of the options selected (so I could require 1-4 schedulers
>> compiled in, but not 0). Unfortunately, the only way that seems allowed
>> is if you compile code in as modules, which Xen does not (with a choice
>> block, you can select multiple items as M, but only 1 as Y, but at least
>> 1 must be present --- since we only support Y, the choice block wouldn't
>> work for the schedulers).
> 
> Perhaps credit should just not be configurable then?
> 
> Jan
> 

How much effort are we willing to put in saving someone? We've already
got these options completely hidden away. We've already given the user a
warning that what they're doing isn't supported and they shouldn't be
touching this. Then they have to disable the scheduler that they pick as
the default. How many people are we expecting to really do this? I'm all
for idiot proofing things but at some point we've got to say there's
enough barriers to prevent this from happening. Otherwise we need to put
a Xen developer in every Xen users home or office.
Jonathan Creekmore Jan. 8, 2016, 5:04 p.m. UTC | #10
Doug Goldstein writes:

> On 1/8/16 10:49 AM, Jan Beulich wrote:
>>>>> On 08.01.16 at 17:30, <jonathan.creekmore@gmail.com> wrote:
>>> So, based on the Kconfig setup and the linker ASSERT, there should be no
>>> way to have a default scheduler that is not in the build. I wish Kconfig
>>> allowed you to state that you must have at least one option selected or
>>> up to all of the options selected (so I could require 1-4 schedulers
>>> compiled in, but not 0). Unfortunately, the only way that seems allowed
>>> is if you compile code in as modules, which Xen does not (with a choice
>>> block, you can select multiple items as M, but only 1 as Y, but at least
>>> 1 must be present --- since we only support Y, the choice block wouldn't
>>> work for the schedulers).
>>
>> Perhaps credit should just not be configurable then?
>>
>> Jan
>>
>
> How much effort are we willing to put in saving someone? We've already
> got these options completely hidden away. We've already given the user a
> warning that what they're doing isn't supported and they shouldn't be
> touching this. Then they have to disable the scheduler that they pick as
> the default. How many people are we expecting to really do this? I'm all
> for idiot proofing things but at some point we've got to say there's
> enough barriers to prevent this from happening. Otherwise we need to put
> a Xen developer in every Xen users home or office.

At this point, with the (not submitted yet) ASSERT in the linker file,
it is a compile error to not have any schedulers linked in and Kconfig
enforces that only schedulers compiled in can be a default.
Andrew Cooper Jan. 8, 2016, 5:13 p.m. UTC | #11
On 08/01/16 17:04, Jonathan Creekmore wrote:
> Doug Goldstein writes:
>
>> On 1/8/16 10:49 AM, Jan Beulich wrote:
>>>>>> On 08.01.16 at 17:30, <jonathan.creekmore@gmail.com> wrote:
>>>> So, based on the Kconfig setup and the linker ASSERT, there should be no
>>>> way to have a default scheduler that is not in the build. I wish Kconfig
>>>> allowed you to state that you must have at least one option selected or
>>>> up to all of the options selected (so I could require 1-4 schedulers
>>>> compiled in, but not 0). Unfortunately, the only way that seems allowed
>>>> is if you compile code in as modules, which Xen does not (with a choice
>>>> block, you can select multiple items as M, but only 1 as Y, but at least
>>>> 1 must be present --- since we only support Y, the choice block wouldn't
>>>> work for the schedulers).
>>> Perhaps credit should just not be configurable then?
>>>
>>> Jan
>>>
>> How much effort are we willing to put in saving someone? We've already
>> got these options completely hidden away. We've already given the user a
>> warning that what they're doing isn't supported and they shouldn't be
>> touching this. Then they have to disable the scheduler that they pick as
>> the default. How many people are we expecting to really do this? I'm all
>> for idiot proofing things but at some point we've got to say there's
>> enough barriers to prevent this from happening. Otherwise we need to put
>> a Xen developer in every Xen users home or office.
> At this point, with the (not submitted yet) ASSERT in the linker file,
> it is a compile error to not have any schedulers linked in and Kconfig
> enforces that only schedulers compiled in can be a default.

I think that should be sufficient.  A user has to go a long way out of
their way to get into this situation in the first place.


If there is a nice way for checking for an empty string in the
preprocessor, then something like

BUILD_BUG_ON(ARRAY_SIZE(CONFIG_SCHED_DEFAULT) == 1);

would also be a good sanity check, but I doubt this specific example
compiles.

~Andrew
Konrad Rzeszutek Wilk Jan. 8, 2016, 5:18 p.m. UTC | #12
On Fri, Jan 08, 2016 at 11:04:56AM -0600, Jonathan Creekmore wrote:
> 
> Doug Goldstein writes:
> 
> > On 1/8/16 10:49 AM, Jan Beulich wrote:
> >>>>> On 08.01.16 at 17:30, <jonathan.creekmore@gmail.com> wrote:
> >>> So, based on the Kconfig setup and the linker ASSERT, there should be no
> >>> way to have a default scheduler that is not in the build. I wish Kconfig
> >>> allowed you to state that you must have at least one option selected or
> >>> up to all of the options selected (so I could require 1-4 schedulers
> >>> compiled in, but not 0). Unfortunately, the only way that seems allowed
> >>> is if you compile code in as modules, which Xen does not (with a choice
> >>> block, you can select multiple items as M, but only 1 as Y, but at least
> >>> 1 must be present --- since we only support Y, the choice block wouldn't
> >>> work for the schedulers).
> >>
> >> Perhaps credit should just not be configurable then?
> >>
> >> Jan
> >>
> >
> > How much effort are we willing to put in saving someone? We've already
> > got these options completely hidden away. We've already given the user a
> > warning that what they're doing isn't supported and they shouldn't be
> > touching this. Then they have to disable the scheduler that they pick as
> > the default. How many people are we expecting to really do this? I'm all
> > for idiot proofing things but at some point we've got to say there's
> > enough barriers to prevent this from happening. Otherwise we need to put
> > a Xen developer in every Xen users home or office.
> 
> At this point, with the (not submitted yet) ASSERT in the linker file,
> it is a compile error to not have any schedulers linked in and Kconfig
> enforces that only schedulers compiled in can be a default.

That would be good!
Jan Beulich Jan. 11, 2016, 9:06 a.m. UTC | #13
>>> On 08.01.16 at 17:58, <cardoe@cardoe.com> wrote:
> On 1/8/16 10:49 AM, Jan Beulich wrote:
>>>>> On 08.01.16 at 17:30, <jonathan.creekmore@gmail.com> wrote:
>>> So, based on the Kconfig setup and the linker ASSERT, there should be no
>>> way to have a default scheduler that is not in the build. I wish Kconfig
>>> allowed you to state that you must have at least one option selected or
>>> up to all of the options selected (so I could require 1-4 schedulers
>>> compiled in, but not 0). Unfortunately, the only way that seems allowed
>>> is if you compile code in as modules, which Xen does not (with a choice
>>> block, you can select multiple items as M, but only 1 as Y, but at least
>>> 1 must be present --- since we only support Y, the choice block wouldn't
>>> work for the schedulers).
>> 
>> Perhaps credit should just not be configurable then?
> 
> How much effort are we willing to put in saving someone? We've already
> got these options completely hidden away. We've already given the user a
> warning that what they're doing isn't supported and they shouldn't be
> touching this. Then they have to disable the scheduler that they pick as
> the default. How many people are we expecting to really do this? I'm all
> for idiot proofing things but at some point we've got to say there's
> enough barriers to prevent this from happening. Otherwise we need to put
> a Xen developer in every Xen users home or office.

I personally think that we shouldn't allow .config-s to be produced
that will yield a build failure. No matter whether supported, we'd
expect (as discussed) people to take care of problems themselves,
but we'd also hope for them to contribute back the adjustments
they had to make. I.e. there's need to be a way for someone to
fix the build issue here, and since we're already aware of the issue
I can't see why we should allow in the brokenness. The precautions
are only against issues we didn't happen to notice.

Jan
diff mbox

Patch

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 046e257..db7411b 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -51,4 +51,71 @@  config KEXEC
 
 	  If unsure, say Y.
 
+# Enable schedulers
+menu "Schedulers"
+	visible if EXPERT = "y"
+
+config SCHED_CREDIT
+	bool "Credit scheduler support"
+	default y
+	---help---
+	  The traditional credit scheduler is a general purpose scheduler.
+
+	  If unsure, say Y.
+
+config SCHED_CREDIT2
+	bool "Credit2 scheduler support (EXPERIMENTAL)"
+	default y
+	---help---
+	  The credit2 scheduler is a general purpose scheduler that is
+	  optimized for lower latency and higher VM density.
+
+	  If unsure, say Y.
+
+config SCHED_RTDS
+	bool "RTDS scheduler support (EXPERIMENTAL)"
+	default y
+	---help---
+	  The RTDS scheduler is a soft and firm real-time scheduler for
+	  multicore, targeted for embedded, automotive, graphics and gaming
+	  in the cloud, and general low-latency workloads.
+
+	  If unsure, say N.
+
+config SCHED_ARINC653
+	bool "ARINC653 scheduler support (EXPERIMENTAL)"
+	default y
+	---help---
+	  The ARINC653 scheduler is a hard real-time scheduler for single
+	  cores, targeted for avionics, drones, and medical devices.
+
+	  If unsure, say N.
+
+choice
+	prompt "Default Scheduler?"
+	default SCHED_CREDIT_DEFAULT if SCHED_CREDIT
+	default SCHED_CREDIT2_DEFAULT if SCHED_CREDIT2
+	default SCHED_RTDS_DEFAULT if SCHED_RTDS
+	default SCHED_ARINC653_DEFAULT if SCHED_ARINC653
+
+	config SCHED_CREDIT_DEFAULT
+		bool "Credit Scheduler" if SCHED_CREDIT
+	config SCHED_CREDIT2_DEFAULT
+		bool "Credit2 Scheduler" if SCHED_CREDIT2
+	config SCHED_RTDS_DEFAULT
+		bool "RT Scheduler" if SCHED_RTDS
+	config SCHED_ARINC653_DEFAULT
+		bool "ARINC653 Scheduler" if SCHED_ARINC653
+endchoice
+
+config SCHED_DEFAULT
+	string
+	default "credit" if SCHED_CREDIT_DEFAULT
+	default "credit2" if SCHED_CREDIT2_DEFAULT
+	default "rtds" if SCHED_RTDS_DEFAULT
+	default "arinc653" if SCHED_ARINC653_DEFAULT
+	default "credit"
+
+endmenu
+
 endmenu
diff --git a/xen/common/Makefile b/xen/common/Makefile
index 8ab15ba..29a5916 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -30,10 +30,10 @@  obj-y += rangeset.o
 obj-y += radix-tree.o
 obj-y += rbtree.o
 obj-y += rcupdate.o
-obj-y += sched_credit.o
-obj-y += sched_credit2.o
-obj-y += sched_arinc653.o
-obj-y += sched_rt.o
+obj-$(CONFIG_SCHED_ARINC653) += sched_arinc653.o
+obj-$(CONFIG_SCHED_CREDIT) += sched_credit.o
+obj-$(CONFIG_SCHED_CREDIT2) += sched_credit2.o
+obj-$(CONFIG_SCHED_RTDS) += sched_rt.o
 obj-y += schedule.o
 obj-y += shutdown.o
 obj-y += softirq.o
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index d121896..2f98a48 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -38,8 +38,8 @@ 
 #include <public/sched.h>
 #include <xsm/xsm.h>
 
-/* opt_sched: scheduler - default to credit */
-static char __initdata opt_sched[10] = "credit";
+/* opt_sched: scheduler - default to configured value */
+static char __initdata opt_sched[10] = CONFIG_SCHED_DEFAULT;
 string_param("sched", opt_sched);
 
 /* if sched_smt_power_savings is set,
@@ -65,10 +65,18 @@  DEFINE_PER_CPU(struct schedule_data, schedule_data);
 DEFINE_PER_CPU(struct scheduler *, scheduler);
 
 static const struct scheduler *schedulers[] = {
+#ifdef CONFIG_SCHED_CREDIT
     &sched_credit_def,
+#endif
+#ifdef CONFIG_SCHED_CREDIT2
     &sched_credit2_def,
+#endif
+#ifdef CONFIG_SCHED_ARINC653
     &sched_arinc653_def,
+#endif
+#ifdef CONFIG_SCHED_RTDS
     &sched_rtds_def,
+#endif
 };
 
 static struct scheduler __read_mostly ops;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index fc61fc3..246338e 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -850,8 +850,13 @@  static inline bool_t is_vcpu_online(const struct vcpu *v)
     return !test_bit(_VPF_down, &v->pause_flags);
 }
 
+#ifdef CONFIG_SCHED_CREDIT
 void set_vcpu_migration_delay(unsigned int delay);
 unsigned int get_vcpu_migration_delay(void);
+#else
+static inline void set_vcpu_migration_delay(unsigned int delay) { }
+static inline unsigned int get_vcpu_migration_delay(void) { return 0; }
+#endif
 
 extern bool_t sched_smt_power_savings;