[PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[vanshikonda]

From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>

Increase the default value of NR_CPUS to 512 from 256. This will
enable the defconfig kernel to support platforms that have upto
512 cores.

Signed-off-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
---
 arch/arm64/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 05e17351e4f3..23fbbf413f58 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -983,7 +983,7 @@ config SCHED_SMT
 config NR_CPUS
 	int "Maximum number of CPUs (2-4096)"
 	range 2 4096
-	default "256"
+	default "512"
 
 config HOTPLUG_CPU
 	bool "Support for hot-pluggable CPUs"
-- 
2.29.2

[PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[vanshikonda]

From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>

Increase the default value of NR_CPUS to 512 from 256. This will
enable the defconfig kernel to support platforms that have upto
512 cores.

Signed-off-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
---
 arch/arm64/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 05e17351e4f3..23fbbf413f58 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -983,7 +983,7 @@ config SCHED_SMT
 config NR_CPUS
 	int "Maximum number of CPUs (2-4096)"
 	range 2 4096
-	default "256"
+	default "512"
 
 config HOTPLUG_CPU
 	bool "Support for hot-pluggable CPUs"
-- 
2.29.2


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Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Will Deacon]

On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> 
> Increase the default value of NR_CPUS to 512 from 256. This will
> enable the defconfig kernel to support platforms that have upto
> 512 cores.

Do we already support such a platform, and what is it? I'm fine with bumping
the number, it's just nice to be able to say specifically _why_ we're dong
it.

Thanks,

Will

Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Will Deacon]

On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> 
> Increase the default value of NR_CPUS to 512 from 256. This will
> enable the defconfig kernel to support platforms that have upto
> 512 cores.

Do we already support such a platform, and what is it? I'm fine with bumping
the number, it's just nice to be able to say specifically _why_ we're dong
it.

Thanks,

Will

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Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Vanshidhar Konda]

On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>>
>> Increase the default value of NR_CPUS to 512 from 256. This will
>> enable the defconfig kernel to support platforms that have upto
>> 512 cores.
>
>Do we already support such a platform, and what is it? I'm fine with bumping
>the number, it's just nice to be able to say specifically _why_ we're dong
>it.

I'm not aware of any publicly available systems that run into the 256
core limitation. At Ampere we have internal systems that would benefit
from this change as they support more than 256 cores.

Thanks,
Vanshi

>
>Thanks,
>
>Will

Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Vanshidhar Konda]

On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>>
>> Increase the default value of NR_CPUS to 512 from 256. This will
>> enable the defconfig kernel to support platforms that have upto
>> 512 cores.
>
>Do we already support such a platform, and what is it? I'm fine with bumping
>the number, it's just nice to be able to say specifically _why_ we're dong
>it.

I'm not aware of any publicly available systems that run into the 256
core limitation. At Ampere we have internal systems that would benefit
from this change as they support more than 256 cores.

Thanks,
Vanshi

>
>Thanks,
>
>Will

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Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Randy Dunlap]

On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
> On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>>>
>>> Increase the default value of NR_CPUS to 512 from 256. This will
>>> enable the defconfig kernel to support platforms that have upto
>>> 512 cores.
>>
>> Do we already support such a platform, and what is it? I'm fine with bumping.
>> the number, it's just nice to be able to say specifically _why_ we're dong
>> it.
> 
> I'm not aware of any publicly available systems that run into the 256
> core limitation. At Ampere we have internal systems that would benefit
> from this change as they support more than 256 cores.

But what does that have to do with the default value?
Do you expect to run defconfig kernels?
I don't ever expect that.

-- 
~Randy

Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Randy Dunlap]

On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
> On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>>>
>>> Increase the default value of NR_CPUS to 512 from 256. This will
>>> enable the defconfig kernel to support platforms that have upto
>>> 512 cores.
>>
>> Do we already support such a platform, and what is it? I'm fine with bumping.
>> the number, it's just nice to be able to say specifically _why_ we're dong
>> it.
> 
> I'm not aware of any publicly available systems that run into the 256
> core limitation. At Ampere we have internal systems that would benefit
> from this change as they support more than 256 cores.

But what does that have to do with the default value?
Do you expect to run defconfig kernels?
I don't ever expect that.

-- 
~Randy


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Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Vanshi Konda]

On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
>[EXTERNAL EMAIL NOTICE: This email originated from an external sender. Please be mindful of safe email handling and proprietary information protection practices.]
>
>
>On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
>> On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>>> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>>>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>>>>
>>>> Increase the default value of NR_CPUS to 512 from 256. This will
>>>> enable the defconfig kernel to support platforms that have upto
>>>> 512 cores.
>>>
>>> Do we already support such a platform, and what is it? I'm fine with bumping.
>>> the number, it's just nice to be able to say specifically _why_ we're dong
>>> it.
>>
>> I'm not aware of any publicly available systems that run into the 256
>> core limitation. At Ampere we have internal systems that would benefit
>> from this change as they support more than 256 cores.
>
>But what does that have to do with the default value?
>Do you expect to run defconfig kernels?
>I don't ever expect that.

Sorry. I should have been more clear in my earlier statement. We
currently have systems in development internally, to be available
publicly later, that support more than 256 cores. Given the time it
takes for a kernel version to be adopted by distros it makes sense to
change the defconfig now rather than later.


Thanks,
Vanshi

>
>--
>~Randy
>

Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Vanshi Konda]

On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
>[EXTERNAL EMAIL NOTICE: This email originated from an external sender. Please be mindful of safe email handling and proprietary information protection practices.]
>
>
>On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
>> On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>>> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>>>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>>>>
>>>> Increase the default value of NR_CPUS to 512 from 256. This will
>>>> enable the defconfig kernel to support platforms that have upto
>>>> 512 cores.
>>>
>>> Do we already support such a platform, and what is it? I'm fine with bumping.
>>> the number, it's just nice to be able to say specifically _why_ we're dong
>>> it.
>>
>> I'm not aware of any publicly available systems that run into the 256
>> core limitation. At Ampere we have internal systems that would benefit
>> from this change as they support more than 256 cores.
>
>But what does that have to do with the default value?
>Do you expect to run defconfig kernels?
>I don't ever expect that.

Sorry. I should have been more clear in my earlier statement. We
currently have systems in development internally, to be available
publicly later, that support more than 256 cores. Given the time it
takes for a kernel version to be adopted by distros it makes sense to
change the defconfig now rather than later.


Thanks,
Vanshi

>
>--
>~Randy
>

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Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Catalin Marinas]

On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
> On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
> > On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
> >> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
> >>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> >>>
> >>> Increase the default value of NR_CPUS to 512 from 256. This will
> >>> enable the defconfig kernel to support platforms that have upto
> >>> 512 cores.
> >>
> >> Do we already support such a platform, and what is it? I'm fine with bumping.
> >> the number, it's just nice to be able to say specifically _why_ we're dong
> >> it.
> > 
> > I'm not aware of any publicly available systems that run into the 256
> > core limitation. At Ampere we have internal systems that would benefit
> > from this change as they support more than 256 cores.
> 
> But what does that have to do with the default value?
> Do you expect to run defconfig kernels?
> I don't ever expect that.

We still aim for the arm64 defconfig to run on all supported SoCs, even
if not optimally. Distros indeed tweak the config to their needs.

-- 
Catalin

Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Catalin Marinas]

On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
> On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
> > On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
> >> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
> >>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> >>>
> >>> Increase the default value of NR_CPUS to 512 from 256. This will
> >>> enable the defconfig kernel to support platforms that have upto
> >>> 512 cores.
> >>
> >> Do we already support such a platform, and what is it? I'm fine with bumping.
> >> the number, it's just nice to be able to say specifically _why_ we're dong
> >> it.
> > 
> > I'm not aware of any publicly available systems that run into the 256
> > core limitation. At Ampere we have internal systems that would benefit
> > from this change as they support more than 256 cores.
> 
> But what does that have to do with the default value?
> Do you expect to run defconfig kernels?
> I don't ever expect that.

We still aim for the arm64 defconfig to run on all supported SoCs, even
if not optimally. Distros indeed tweak the config to their needs.

-- 
Catalin

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Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Vanshidhar Konda]

On Mon, Jan 11, 2021 at 06:25:27PM +0000, Catalin Marinas wrote:
>On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
>> On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
>> > On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>> >> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>> >>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>> >>>
>> >>> Increase the default value of NR_CPUS to 512 from 256. This will
>> >>> enable the defconfig kernel to support platforms that have upto
>> >>> 512 cores.
>> >>
>> >> Do we already support such a platform, and what is it? I'm fine with bumping.
>> >> the number, it's just nice to be able to say specifically _why_ we're dong
>> >> it.
>> >
>> > I'm not aware of any publicly available systems that run into the 256
>> > core limitation. At Ampere we have internal systems that would benefit
>> > from this change as they support more than 256 cores.
>>
>> But what does that have to do with the default value?
>> Do you expect to run defconfig kernels?
>> I don't ever expect that.
>
>We still aim for the arm64 defconfig to run on all supported SoCs, even
>if not optimally. Distros indeed tweak the config to their needs.

Would "all supported SoCs" mean only SoCs that are currently available
publicly? Could we include support for SoCs/systems in development but
to be available publicly in the next few years?

Thanks,
Vanshi

>
>-- 
>Catalin

Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Vanshidhar Konda]

On Mon, Jan 11, 2021 at 06:25:27PM +0000, Catalin Marinas wrote:
>On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
>> On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
>> > On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
>> >> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
>> >>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
>> >>>
>> >>> Increase the default value of NR_CPUS to 512 from 256. This will
>> >>> enable the defconfig kernel to support platforms that have upto
>> >>> 512 cores.
>> >>
>> >> Do we already support such a platform, and what is it? I'm fine with bumping.
>> >> the number, it's just nice to be able to say specifically _why_ we're dong
>> >> it.
>> >
>> > I'm not aware of any publicly available systems that run into the 256
>> > core limitation. At Ampere we have internal systems that would benefit
>> > from this change as they support more than 256 cores.
>>
>> But what does that have to do with the default value?
>> Do you expect to run defconfig kernels?
>> I don't ever expect that.
>
>We still aim for the arm64 defconfig to run on all supported SoCs, even
>if not optimally. Distros indeed tweak the config to their needs.

Would "all supported SoCs" mean only SoCs that are currently available
publicly? Could we include support for SoCs/systems in development but
to be available publicly in the next few years?

Thanks,
Vanshi

>
>-- 
>Catalin

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Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Will Deacon]

On Mon, Jan 11, 2021 at 09:20:03PM -0800, Vanshidhar Konda wrote:
> On Mon, Jan 11, 2021 at 06:25:27PM +0000, Catalin Marinas wrote:
> > On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
> > > On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
> > > > On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
> > > >> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
> > > >>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> > > >>>
> > > >>> Increase the default value of NR_CPUS to 512 from 256. This will
> > > >>> enable the defconfig kernel to support platforms that have upto
> > > >>> 512 cores.
> > > >>
> > > >> Do we already support such a platform, and what is it? I'm fine with bumping.
> > > >> the number, it's just nice to be able to say specifically _why_ we're dong
> > > >> it.
> > > >
> > > > I'm not aware of any publicly available systems that run into the 256
> > > > core limitation. At Ampere we have internal systems that would benefit
> > > > from this change as they support more than 256 cores.
> > > 
> > > But what does that have to do with the default value?
> > > Do you expect to run defconfig kernels?
> > > I don't ever expect that.
> > 
> > We still aim for the arm64 defconfig to run on all supported SoCs, even
> > if not optimally. Distros indeed tweak the config to their needs.
> 
> Would "all supported SoCs" mean only SoCs that are currently available
> publicly? Could we include support for SoCs/systems in development but
> to be available publicly in the next few years?

I don't really see the need to rush that into defconfig, so I'd prefer
to make the update when something actually exists otherwise it's really
hard to keep track of why we made the decision (especially as unreleased
hardware is liable to change).

Will

Re: [PATCH] arm64: Kconfig: Increase NR_CPUS default to 512

[Will Deacon]

On Mon, Jan 11, 2021 at 09:20:03PM -0800, Vanshidhar Konda wrote:
> On Mon, Jan 11, 2021 at 06:25:27PM +0000, Catalin Marinas wrote:
> > On Mon, Jan 11, 2021 at 10:03:18AM -0800, Randy Dunlap wrote:
> > > On 1/11/21 9:57 AM, Vanshidhar Konda wrote:
> > > > On Mon, Jan 11, 2021 at 10:56:36AM +0000, Will Deacon wrote:
> > > >> On Sat, Jan 09, 2021 at 09:36:15PM -0800, vanshikonda@os.amperecomputing.com wrote:
> > > >>> From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> > > >>>
> > > >>> Increase the default value of NR_CPUS to 512 from 256. This will
> > > >>> enable the defconfig kernel to support platforms that have upto
> > > >>> 512 cores.
> > > >>
> > > >> Do we already support such a platform, and what is it? I'm fine with bumping.
> > > >> the number, it's just nice to be able to say specifically _why_ we're dong
> > > >> it.
> > > >
> > > > I'm not aware of any publicly available systems that run into the 256
> > > > core limitation. At Ampere we have internal systems that would benefit
> > > > from this change as they support more than 256 cores.
> > > 
> > > But what does that have to do with the default value?
> > > Do you expect to run defconfig kernels?
> > > I don't ever expect that.
> > 
> > We still aim for the arm64 defconfig to run on all supported SoCs, even
> > if not optimally. Distros indeed tweak the config to their needs.
> 
> Would "all supported SoCs" mean only SoCs that are currently available
> publicly? Could we include support for SoCs/systems in development but
> to be available publicly in the next few years?

I don't really see the need to rush that into defconfig, so I'd prefer
to make the update when something actually exists otherwise it's really
hard to keep track of why we made the decision (especially as unreleased
hardware is liable to change).

Will

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