Re: [PATCH] arm64: NUMA: Kconfig: Increase max number of nodes
From: Vanshidhar Konda
Date: Tue Oct 27 2020 - 21:48:38 EST
On Thu, Oct 22, 2020 at 12:21:27PM +0100, Robin Murphy wrote:
On 2020-10-22 02:07, Vanshi Konda wrote:
On Thu, Oct 22, 2020 at 12:44:15AM +0100, Robin Murphy wrote:
On 2020-10-21 12:02, Jonathan Cameron wrote:
On Wed, 21 Oct 2020 09:43:21 +0530
Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote:
On 10/20/2020 11:39 PM, Valentin Schneider wrote:
Hi,
Nit on the subject: this only increases the default, the max
is still 2?????.
Agreed.
On 20/10/20 18:34, Vanshidhar Konda wrote:
The current arm64 max NUMA nodes default to 4. Today's
arm64 systems can
reach or exceed 16. Increase the number to 64 (matching x86_64).
Signed-off-by: Vanshidhar Konda <vanshikonda@xxxxxxxxxxxxxxxxxxxxxx>
---
??arch/arm64/Kconfig | 2 +-
??1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 893130ce1626..3e69d3c981be 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -980,7 +980,7 @@ config NUMA
??config NODES_SHIFT
?????????? int "Maximum NUMA Nodes (as a power of 2)"
?????????? range 1 10
-?????? default "2"
+?????? default "6"
This leads to more statically allocated memory for things
like node to CPU
maps (see uses of MAX_NUMNODES), but that shouldn't be too much of an
issue.
The smaller systems should not be required to waste those memory in
a default case, unless there is a real and available larger system
with those increased nodes.
AIUI this also directly correlates to how many more
page->flags bits are
required: are we sure the max 10 works on any aarch64 platform? I'm
We will have to test that. Besides 256 (2 ^ 8) is the first threshold
to be crossed here.
genuinely asking here, given that I'm mostly a stranger to the mm
world. The default should be something we're somewhat confident works
everywhere.
Agreed. Do we really need to match X86 right now ? Do we really have
systems that has 64 nodes ? We should not increase the default node
value and then try to solve some new problems, when there might not
be any system which could even use that. I would suggest increase
NODES_SHIFT value upto as required by a real and available system.
I'm not going to give precise numbers on near future systems but
it is public
that we ship 8 NUMA node ARM64 systems today.?? Things will get more
interesting as CXL and CCIX enter the market on ARM systems,
given chances are every CXL device will look like another NUMA
node (CXL spec says they should be presented as such) and you
may be able to rack up lots of them.
So I'd argue minimum that makes sense today is 16 nodes, but
looking forward
even a little and 64 is not a great stretch.
I'd make the jump to 64 so we can forget about this again for a
year or two.
People will want to run today's distros on these new machines and we'd
rather not have to go around all the distros asking them to
carry a patch
increasing this count (I assume they are already carrying such a patch
due to those 8 node systems)
To echo Jonathan's statement above we are looking at systems that will
need approximately 64 NUMA nodes over the next 5-6 years - the time for
which an LTS kernel would be maintained. Some of the reason's for
increasing NUMA nodes during this time period include CXL, CCIX and
NVDIMM (like Jonathan pointed out).
The main argument against increasing the NODES_SHIFT seems to be a
concern that it negatively impacts other ARM64 systems. Could anyone
share what kind of systems we are talking about? For a system that has
NEED_MULTIPLE_NODES set, would the impact be noticeable?
Systems like the ESPRESSObin - sure, sane people aren't trying to run
desktops or development environments in 1GB of RAM, but it's not
uncommon for them to use a minimal headless install of their favourite
generic arm64 distro rather than something more "embedded" like
OpenWrt or Armbian. Increasing a generic kernel's memory footprint
(and perhaps more importantly, cache footprint) more than necessary is
going to have *some* impact.
Ampere’s platforms support multiple NUMA configuration options to meet
different customer requirements. Multiple configurations have more than
4 (currrent default) NUMA nodes. These fail to initialize NUMA with the
following errors in dmesg:
[ 0.000000] ACPI: SRAT: Too many proximity domains.
[ 0.000000] ACPI: SRAT: SRAT not used.
[ 0.000000] SRAT: Invalid NUMA node -1 in ITS affinity
[ 0.000000] SRAT: Invalid NUMA node -1 in ITS affinity
If we look at the forecast for the next LTS kernel lifetime, the number
of NUMA nodes will increase significantly due to SOCs with significantly
higher core counts, increased number of memory channels, and new devices
such as CCIX attached memory, etc. Supporting these platforms with a
default kernel config will require a minimum NODES_SHIFT value = 6.
Vanshi
Robin.
Vanshi
Nit: I doubt any sane distro is going to carry a patch to adjust
the *default* value of a Kconfig option. They might tune the
actual value in their config, but, well, isn't that the whole
point of configs? ;)
Robin.
Jonathan
?????????? depends on NEED_MULTIPLE_NODES
?????????? help
?????????????? Specify the maximum number of NUMA Nodes
available on the target
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