[PATCH 1/3] Make credit2 the default scheduler

[PATCH 1/3] Make credit2 the default scheduler

[George Dunlap]

Credit2 was declared "supported" in 4.8, and as of 4.10 had two other
critical features implemented (soft affinity / NUMA and caps).

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
---
CC: Ian Jackson <ian.jackson@citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Jan Beulich <jbeulich@suse.com>
CC: Tim Deegan <tim@xen.org>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Konrad Wilk <konrad.wilk@oracle.com>
CC: Dario Faggioli <dfaggioli@suse.com>
---
 xen/common/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 103ef44cb5..3d20a9231f 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -200,7 +200,7 @@ config SCHED_NULL
 
 choice
 	prompt "Default Scheduler?"
-	default SCHED_CREDIT_DEFAULT
+	default SCHED_CREDIT2_DEFAULT
 
 	config SCHED_CREDIT_DEFAULT
 		bool "Credit Scheduler" if SCHED_CREDIT
@@ -221,7 +221,7 @@ config SCHED_DEFAULT
 	default "rtds" if SCHED_RTDS_DEFAULT
 	default "arinc653" if SCHED_ARINC653_DEFAULT
 	default "null" if SCHED_NULL_DEFAULT
-	default "credit"
+	default "credit2"
 
 endmenu
 
-- 
2.15.1


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[PATCH 2/3] xen: Fix credit1 Kconfig entry

[George Dunlap]

...so that it shows up in the menu and can be disabled.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
---
CC: Ian Jackson <ian.jackson@citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Jan Beulich <jbeulich@suse.com>
CC: Tim Deegan <tim@xen.org>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Konrad Wilk <konrad.wilk@oracle.com>
---
 xen/common/Kconfig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 3d20a9231f..131318d63a 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -164,7 +164,8 @@ menu "Schedulers"
 	visible if EXPERT = "y"
 
 config SCHED_CREDIT
-	def_bool y
+	bool "Credit scheduler support"
+	default y
 	---help---
 	  The traditional credit scheduler is a general purpose scheduler.
 
-- 
2.15.1


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Re: [PATCH 2/3] xen: Fix credit1 Kconfig entry

[Jan Beulich]

>>> On 05.02.18 at 12:36, <george.dunlap@citrix.com> wrote:
> ...so that it shows up in the menu and can be disabled.
> 
> Signed-off-by: George Dunlap <george.dunlap@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>



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Re: [PATCH 2/3] xen: Fix credit1 Kconfig entry

[Dario Faggioli]

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On Mon, 2018-02-05 at 06:35 -0700, Jan Beulich wrote:
> > > > On 05.02.18 at 12:36, <george.dunlap@citrix.com> wrote:
> > 
> > ...so that it shows up in the menu and can be disabled.
> > 
> > Signed-off-by: George Dunlap <george.dunlap@citrix.com>
> 
> Acked-by: Jan Beulich <jbeulich@suse.com>
> 
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>

Regards,
Dario
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-----------------------------------------------------------------
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[PATCH 3/3] xen: Disable ARINC653 scheduler by default for non-DEBUG builds

[George Dunlap]

The ARINC653 scheduler is targeted at a very specific niche; typical
users cannot benefit from using it.  Disable it by default for
non-DEBUG builds.  (Enable it for DEBUG builds so that we catch any
build breakages sooner rather than later.)

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
---
CC: Ian Jackson <ian.jackson@citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Jan Beulich <jbeulich@suse.com>
CC: Tim Deegan <tim@xen.org>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Konrad Wilk <konrad.wilk@oracle.com>
CC: Josh Whitehead <josh.whitehead@dornerworks.com>
CC: Robert VanVossen <robert.vanvossen@dornerworks.com>
---
 xen/common/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 131318d63a..82a34c5d79 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -186,7 +186,7 @@ config SCHED_RTDS
 
 config SCHED_ARINC653
 	bool "ARINC653 scheduler support (EXPERIMENTAL)"
-	default y
+	default DEBUG
 	---help---
 	  The ARINC653 scheduler is a hard real-time scheduler for single
 	  cores, targeted for avionics, drones, and medical devices.
-- 
2.15.1


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Re: [PATCH 3/3] xen: Disable ARINC653 scheduler by default for non-DEBUG builds

[Jan Beulich]

>>> On 05.02.18 at 12:36, <george.dunlap@citrix.com> wrote:
> The ARINC653 scheduler is targeted at a very specific niche; typical
> users cannot benefit from using it.  Disable it by default for
> non-DEBUG builds.

The more that its prompt says "(EXPERIMENTAL)".

> Signed-off-by: George Dunlap <george.dunlap@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>



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Re: [PATCH 3/3] xen: Disable ARINC653 scheduler by default for non-DEBUG builds

[George Dunlap]

On 02/05/2018 01:36 PM, Jan Beulich wrote:
>>>> On 05.02.18 at 12:36, <george.dunlap@citrix.com> wrote:
>> The ARINC653 scheduler is targeted at a very specific niche; typical
>> users cannot benefit from using it.  Disable it by default for
>> non-DEBUG builds.
> 
> The more that its prompt says "(EXPERIMENTAL)".

Well I left RTDS on by default, since there would be a small chance
someone might want to play with it.  But AFAICT ARINC653 isn't really
something designed to be used by anyone outside a very specific set of
users.

 -George

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Re: [PATCH 3/3] xen: Disable ARINC653 scheduler by default for non-DEBUG builds

[Dario Faggioli]

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On Mon, 2018-02-05 at 06:36 -0700, Jan Beulich wrote:
> > > > On 05.02.18 at 12:36, <george.dunlap@citrix.com> wrote:
> > 
> > The ARINC653 scheduler is targeted at a very specific niche;
> > typical
> > users cannot benefit from using it.  Disable it by default for
> > non-DEBUG builds.
> 
> The more that its prompt says "(EXPERIMENTAL)".
> 
> > Signed-off-by: George Dunlap <george.dunlap@citrix.com>
> 
> Acked-by: Jan Beulich <jbeulich@suse.com>
> 
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>

Regards,
Dario
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-----------------------------------------------------------------
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Software Engineer @ SUSE https://www.suse.com/

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Re: [PATCH 3/3] xen: Disable ARINC653 scheduler by default for non-DEBUG builds

[George Dunlap]

On 02/05/2018 02:42 PM, Dario Faggioli wrote:
> On Mon, 2018-02-05 at 06:36 -0700, Jan Beulich wrote:
>>>>> On 05.02.18 at 12:36, <george.dunlap@citrix.com> wrote:
>>>
>>> The ARINC653 scheduler is targeted at a very specific niche;
>>> typical
>>> users cannot benefit from using it.  Disable it by default for
>>> non-DEBUG builds.
>>
>> The more that its prompt says "(EXPERIMENTAL)".
>>
>>> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
>>
>> Acked-by: Jan Beulich <jbeulich@suse.com>
>>
> Reviewed-by: Dario Faggioli <dfaggioli@suse.com>

Just to let people know, I was planning on waiting at least a few days
for the maintainers of this scheduler to express an opinion before
checking it in.

 -Georeg

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Re: [PATCH 1/3] Make credit2 the default scheduler

[Andrew Cooper]

On 05/02/18 11:36, George Dunlap wrote:
> Credit2 was declared "supported" in 4.8, and as of 4.10 had two other
> critical features implemented (soft affinity / NUMA and caps).
>
> Signed-off-by: George Dunlap <george.dunlap@citrix.com>

On what justification?

Switching the default involves demonstrating that the new default is
better than the old one, and simply "we've implemented more features"
isn't good enough IMO.

The last set of measurements I recall seeing said that credit1 and
credit2 were mostly kneck-and-kneck, but there was still a noticeable
difference in credit1's favour when it came to aggregate small-packet
TCP throughput, and no benchmark where credit2 was clearly a winner.

~Andrew

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Re: [PATCH 1/3] Make credit2 the default scheduler

[George Dunlap]

On 02/05/2018 11:45 AM, Andrew Cooper wrote:
> On 05/02/18 11:36, George Dunlap wrote:
>> Credit2 was declared "supported" in 4.8, and as of 4.10 had two other
>> critical features implemented (soft affinity / NUMA and caps).
>>
>> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
> 
> On what justification?
> 
> Switching the default involves demonstrating that the new default is
> better than the old one, and simply "we've implemented more features"
> isn't good enough IMO.

Well the code is certainly better: more predictable, less jitter, easier
to determine how modifications will affect overall behavior, easier in
the future to make load-balancing behavior more subtle (e.g., taking
into account the cost of powering up extra cores, &c).

> The last set of measurements I recall seeing said that credit1 and
> credit2 were mostly kneck-and-kneck, but there was still a noticeable
> difference in credit1's favour when it came to aggregate small-packet
> TCP throughput, and no benchmark where credit2 was clearly a winner.

It's somewhat of a mixed bag.  Unfortunately most of what I have are
tests using XenServer's internal perf testing system, so I can't share
the raw data (via links anyway).

Here is a summary of data from an intern e-mail Dario sent about 6
months ago:

* DVDbench: On underloaded systems, credit2 outperformed credit1 by
about 4%.  On overloaded systems, credit2 underperformed by about 3%.

* On a range of tests (unixbench, lmbench, &c), credit and credit2
perform within 5% of each other (up and down).

* Credit2 fairly consistently beats credit for TCP-style workloads.

* Credit2 is sometimes equal to, sometimes 5-15% worse than, credit for
synthetic CPU workloads (e.g., Dhrystone).

* On LoginVSI, credit2 fairly consistently outperforms credit by about 10%.

Credit2, like credit, has a number of workloads / setups for which
performance could be improved.  Personally I think networking and
partially-loaded systems is going to be more representative of what Xen
is actually used for; so I think credit2 is on the whole the better
scheduler to use by default.  And in any case, making those improvements
on credit2 will be easier than on credit.

 -George

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Re: [PATCH 1/3] Make credit2 the default scheduler

[Dario Faggioli]

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On Mon, 2018-02-05 at 13:01 +0000, George Dunlap wrote:
> On 02/05/2018 11:45 AM, Andrew Cooper wrote:
> > 
> Here is a summary of data from an intern e-mail Dario sent about 6
> months ago:
> 
> * DVDbench: On underloaded systems, credit2 outperformed credit1 by
> about 4%.  On overloaded systems, credit2 underperformed by about 3%.
> 
> * On a range of tests (unixbench, lmbench, &c), credit and credit2
> perform within 5% of each other (up and down).
> 
> * Credit2 fairly consistently beats credit for TCP-style workloads.
> 
> * Credit2 is sometimes equal to, sometimes 5-15% worse than, credit
> for
> synthetic CPU workloads (e.g., Dhrystone).
> 
> * On LoginVSI, credit2 fairly consistently outperforms credit by
> about 10%.
> 
Thanks George for summing this up!

> Credit2, like credit, has a number of workloads / setups for which
> performance could be improved.  Personally I think networking and
> partially-loaded systems is going to be more representative of what
> Xen
> is actually used for; so I think credit2 is on the whole the better
> scheduler to use by default.  
>
I'm sure this will sound no surprise for anyone, but allow me to say it
anyway: I agree with George. :-D

> And in any case, making those improvements
> on credit2 will be easier than on credit.
> 
And, if possible, I agree with George on this even more!

One thing I think we should consider, though, is that we've often said
we would switch at the very beginning of a dev cycle, to get as much as
osstest and day-by-day testing from developer as possible.

Considering we're releasing in June, but freezing in March, do we think
 it is still early enough?

Regards,
Dario
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-----------------------------------------------------------------
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Re: [PATCH 1/3] Make credit2 the default scheduler

[Juergen Gross]

On 05/02/18 17:53, Dario Faggioli wrote:
> On Mon, 2018-02-05 at 13:01 +0000, George Dunlap wrote:
>> And in any case, making those improvements
>> on credit2 will be easier than on credit.
>>
> And, if possible, I agree with George on this even more!
> 
> One thing I think we should consider, though, is that we've often said
> we would switch at the very beginning of a dev cycle, to get as much as
> osstest and day-by-day testing from developer as possible.
> 
> Considering we're releasing in June, but freezing in March, do we think
>  it is still early enough?

The 4.11 release is completely dominated by Meltdown/Spectre mitigation
work. So either 4.11 will be a security focused version or we need to
extend the development phase.

I think we should _really_ discuss release schedules rather sooner than
later.


Juergen

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Re: [PATCH 1/3] Make credit2 the default scheduler

[George Dunlap]

On 02/06/2018 06:18 AM, Juergen Gross wrote:
> On 05/02/18 17:53, Dario Faggioli wrote:
>> On Mon, 2018-02-05 at 13:01 +0000, George Dunlap wrote:
>>> And in any case, making those improvements
>>> on credit2 will be easier than on credit.
>>>
>> And, if possible, I agree with George on this even more!
>>
>> One thing I think we should consider, though, is that we've often said
>> we would switch at the very beginning of a dev cycle, to get as much as
>> osstest and day-by-day testing from developer as possible.
>>
>> Considering we're releasing in June, but freezing in March, do we think
>>  it is still early enough?
> 
> The 4.11 release is completely dominated by Meltdown/Spectre mitigation
> work. So either 4.11 will be a security focused version or we need to
> extend the development phase.

Personally I could go either way on this.  So unless someone wants to
argue for switching now (or we significantly extend the development
window), let's plan on leaving this for post-4.11.

> I think we should _really_ discuss release schedules rather sooner than
> later.

Sorry I wasn't much involved in the earlier discussion -- I was rather
heads-down trying to figure out what to do about speculative execution.
:-)  Let me see if I can go find that thread.

 -George

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Re: [PATCH 1/3] Make credit2 the default scheduler

[Dario Faggioli]

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On Tue, 2018-02-06 at 17:02 +0000, George Dunlap wrote:
> On 02/06/2018 06:18 AM, Juergen Gross wrote:
> > On 05/02/18 17:53, Dario Faggioli wrote:
> > > 
> > > Considering we're releasing in June, but freezing in March, do we
> > > think
> > >  it is still early enough?
> 
> > The 4.11 release is completely dominated by Meltdown/Spectre
> > mitigation
> > work. So either 4.11 will be a security focused version or we need
> > to
> > extend the development phase.
> 
> Personally I could go either way on this.  So unless someone wants to
> argue for switching now (or we significantly extend the development
> window), let's plan on leaving this for post-4.11.
> 
Yes, I agree.

And if we don't switch now, I think we should say that, unless someone
argues against your reasoning in your other email, and convince us,
we'll switch as soon as 4.12 is branched (or perhaps as soon as 4.11 is
released?).

Regards,
Dario
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Re: [PATCH 1/3] Make credit2 the default scheduler

[George Dunlap]

On 02/06/2018 10:39 PM, Dario Faggioli wrote:
> On Tue, 2018-02-06 at 17:02 +0000, George Dunlap wrote:
>> On 02/06/2018 06:18 AM, Juergen Gross wrote:
>>> On 05/02/18 17:53, Dario Faggioli wrote:
>>>>
>>>> Considering we're releasing in June, but freezing in March, do we
>>>> think
>>>>  it is still early enough?
>>
>>> The 4.11 release is completely dominated by Meltdown/Spectre
>>> mitigation
>>> work. So either 4.11 will be a security focused version or we need
>>> to
>>> extend the development phase.
>>
>> Personally I could go either way on this.  So unless someone wants to
>> argue for switching now (or we significantly extend the development
>> window), let's plan on leaving this for post-4.11.
>>
> Yes, I agree.
> 
> And if we don't switch now, I think we should say that, unless someone
> argues against your reasoning in your other email, and convince us,
> we'll switch as soon as 4.12 is branched (or perhaps as soon as 4.11 is
> released?).

Well I had planned to do that for 4.11, but something came up. :-)
Hopefully nothing similar will come up this time...

 -George

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