[PATCH] xen/Kconfig: Correct the NR_CPUS description

[PATCH] xen/Kconfig: Correct the NR_CPUS description

[Andrew Cooper]

The description "physical CPUs" is especially wrong, as it implies the number
of sockets, which tops out at 8 on all but the very biggest servers.

NR_CPUS is the number of logical entities the scheduler can use.

Reported-by: hanetzer@startmail.com
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien@xen.org>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
CC: hanetzer@startmail.com
---
 xen/arch/Kconfig | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
index 1954d1c5c1..d144d4c8d3 100644
--- a/xen/arch/Kconfig
+++ b/xen/arch/Kconfig
@@ -1,11 +1,17 @@
 
 config NR_CPUS
-	int "Maximum number of physical CPUs"
+	int "Maximum number of CPUs"
 	range 1 4095
 	default "256" if X86
 	default "8" if ARM && RCAR3
 	default "4" if ARM && QEMU
 	default "4" if ARM && MPSOC
 	default "128" if ARM
-	---help---
-	  Specifies the maximum number of physical CPUs which Xen will support.
+	help
+	  Controls the build-time size of various arrays and bitmaps
+	  associated with multiple-cpu management.  It is the upper bound of
+	  the number of logical entities the scheduler can run code on.
+
+	  For CPU cores which support Simultaneous Multi-Threading or similar
+	  technologies, this the number of logical threads which Xen will
+	  support.
-- 
2.11.0

Re: [PATCH] xen/Kconfig: Correct the NR_CPUS description

[Jan Beulich]

On 19.12.2020 00:38, Andrew Cooper wrote:
> The description "physical CPUs" is especially wrong, as it implies the number
> of sockets, which tops out at 8 on all but the very biggest servers.
> 
> NR_CPUS is the number of logical entities the scheduler can use.
> 
> Reported-by: hanetzer@startmail.com

This wasn't on xen-devel, was it?

> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

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

Re: [PATCH] xen/Kconfig: Correct the NR_CPUS description

[Andrew Cooper]

On 21/12/2020 08:37, Jan Beulich wrote:
> On 19.12.2020 00:38, Andrew Cooper wrote:
>> The description "physical CPUs" is especially wrong, as it implies the number
>> of sockets, which tops out at 8 on all but the very biggest servers.
>>
>> NR_CPUS is the number of logical entities the scheduler can use.
>>
>> Reported-by: hanetzer@startmail.com
> This wasn't on xen-devel, was it?

No.  It was on IRC, hence the rather late patch.

>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Acked-by: Jan Beulich <jbeulich@suse.com>

Thanks.

~Andrew