Hi Peter,
On 9/23/21 10:59, Peter Humphrey wrote:
Hello list,
I see "[ 0.003162] No NUMA configuration found" in dmesg. Does that mean I
should, or can, remove the NUMA settings from the kernel? This is a Ryzen M9
5900X machine.
I have CONFIG_NUMA unset on both of my AMD Ryzen machines (Zen+ and
Zen2) with no issues
You'd need NUMA if you had a NUMA machine. In current context, thatwrote:
would be either a) a dual socket system, b) an amd threadripper, or c)
some of the really high core xeons. If your motherboard doesnt have
certain memory banks allocated to certain processors or cores, you're probably not running a NUMA machine.
NUMA stands for non-uniform memory access, it means that certain
processor cores have more direct access to certain parts of memory
than others do (e.g. to access the other memory they need the other
cpu core to pass it through)
On Thu, 23 Sept 2021 at 19:39, Charlotte Delenk <darkkirb@darkkirb.de>
Hi Peter,
On 9/23/21 10:59, Peter Humphrey wrote:
Hello list,
I see "[ 0.003162] No NUMA configuration found" in dmesg. Does that mean I should, or can, remove the NUMA settings from the kernel? This
is a Ryzen M9 5900X machine.
I have CONFIG_NUMA unset on both of my AMD Ryzen machines (Zen+ and
Zen2) with no issues
You'd need NUMA if you had a NUMA machine. In current context, that
would be either a) a dual socket system, b) an amd threadripper, or
c) some of the really high core xeons. If your motherboard doesnt
have certain memory banks allocated to certain processors or cores,
you're probably not running a NUMA machine.
On 9/23/21 18:30, Grant Taylor wrote:
On 9/23/21 4:39 AM, Miles Malone wrote:
You'd need NUMA if you had a NUMA machine. In current context, that
would be either a) a dual socket system, b) an amd threadripper, or
c) some of the really high core xeons. If your motherboard doesnt
have certain memory banks allocated to certain processors or cores,
you're probably not running a NUMA machine.
Will a kernel without NUMA support boot and run on a system that has a
NUMA architecture?
If it will boot and run, does it simply do so in a sub-optimal way?
Pure speculation for this one but if it works it's probably only going
to detect part of the memory and some of the devices and one cpu, since
the other resources are physically connected to the other cpus.
Flipping the coin on the other side, is there any negative effect
(other than kernel size / lines of code / attack surface) for having
NUMA support enabled on a non-NUMA system?
There is no meaningful downside to leaving it enabled, it's enabled in
many distribution kernels for a reason.
I've booted a kernel with no NUMA config, and it seems to run fine on this single-socket Ryzen motherboard. I just get the one entry in dmesg:
$ dmesg | grep -i numa
[ 0.297998] pci_bus 0000:00: on NUMA node 0
That's it. I'm running five BOINC projects, some of which run on vbox, so on this motherboard it seems clear that I don't need NUMA.
Out of interest, have you tried booting a NUMA enabled kernel to see what dmesg reports?
On an old laptop, which definitely has only a single AMD0x0000000000000000-0x000000042effffff]
APU, I get:
$ dmesg | grep -i NUMA -A2
[ 0.002078] No NUMA configuration found
[ 0.002080] Faking a node at [mem
[ 0.002085] NODE_DATA(0) allocated [mem 0x42effc000-0x42effffff]
On Thursday, 23 September 2021 19:20:52 BST Michael wrote:
Out of interest, have you tried booting a NUMA enabled kernel to see what dmesg reports?
Yes, it's been enabled ever since I had a dual-socket motherboard, years
ago. I didn't understand why I did or didn't need it until I read Miles's post yesterday (thanks, Miles). I don't know why it hadn't been made clear
in any websites I've visited.
On an old laptop, which definitely has only a single AMD
APU, I get:
$ dmesg | grep -i NUMA -A2
[ 0.002078] No NUMA configuration found
[ 0.002080] Faking a node at [mem
0x0000000000000000-0x000000042effffff]
[ 0.002085] NODE_DATA(0) allocated [mem 0x42effc000-0x42effffff]
I had something similar. Oddly, with NUMA configured I get "not found" and without it I get "pci_bus 0000:00: on NUMA node 0". The system seems to run happily either way.
On Friday, 24 September 2021 10:06:49 BST Peter Humphrey wrote:
On Thursday, 23 September 2021 19:20:52 BST Michael wrote:Sorry I should have made it clear - the above "No NUMA configuration found" message was obtained *with* NUMA enabled in my kernel.
Out of interest, have you tried booting a NUMA enabled kernel to see what >>> dmesg reports?Yes, it's been enabled ever since I had a dual-socket motherboard, years
ago. I didn't understand why I did or didn't need it until I read Miles's
post yesterday (thanks, Miles). I don't know why it hadn't been made clear >> in any websites I've visited.
On an old laptop, which definitely has only a single AMD0x0000000000000000-0x000000042effffff]
APU, I get:
$ dmesg | grep -i NUMA -A2
[ 0.002078] No NUMA configuration found
[ 0.002080] Faking a node at [mem
[ 0.002085] NODE_DATA(0) allocated [mem 0x42effc000-0x42effffff]I had something similar. Oddly, with NUMA configured I get "not found" and >> without it I get "pci_bus 0000:00: on NUMA node 0". The system seems to run >> happily either way.
I suppose "NUMA on node 0" is the default first socket, which the kernel sets up. If the kernel can't find a second CPU it will be 'faking' a multi-CPU memory allocation setup, when it comes to allocate memory to the only CPU available. If the kernel does not have NUMA enabled then it doesn't need to fake anything. It will treat the hardware as a single socket MoBo and no further tests would be undertaken. All suppositions of course, I haven't looked at the code. ;-)
On 24/9/21 5:38 pm, Michael wrote:
On Friday, 24 September 2021 10:06:49 BST Peter Humphrey wrote:Try "numactl --hardware" (from the numactl package)
On Thursday, 23 September 2021 19:20:52 BST Michael wrote:Sorry I should have made it clear - the above "No NUMA configuration found" >> message was obtained *with* NUMA enabled in my kernel.
Out of interest, have you tried booting a NUMA enabled kernel to see what >>>> dmesg reports?Yes, it's been enabled ever since I had a dual-socket motherboard, years >>> ago. I didn't understand why I did or didn't need it until I read Miles's >>> post yesterday (thanks, Miles). I don't know why it hadn't been made clear >>> in any websites I've visited.
On an old laptop, which definitely has only a single AMD0x0000000000000000-0x000000042effffff]
APU, I get:
$ dmesg | grep -i NUMA -A2
[ 0.002078] No NUMA configuration found
[ 0.002080] Faking a node at [mem
[ 0.002085] NODE_DATA(0) allocated [mem 0x42effc000-0x42effffff]I had something similar. Oddly, with NUMA configured I get "not found" and >>> without it I get "pci_bus 0000:00: on NUMA node 0". The system seems to run >>> happily either way.
I suppose "NUMA on node 0" is the default first socket, which the kernel sets
up. If the kernel can't find a second CPU it will be 'faking' a multi-CPU >> memory allocation setup, when it comes to allocate memory to the only CPU
available. If the kernel does not have NUMA enabled then it doesn't need to >> fake anything. It will treat the hardware as a single socket MoBo and no
further tests would be undertaken. All suppositions of course, I haven't
looked at the code. ;-)
rattus ~ # numactl --hardware
available: 1 nodes (0)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11
node 0 size: 31942 MB
node 0 free: 7210 MB
node distances:
node 0
0: 10
rattus ~ #
(Intel 6 core - NUMA emulation in the kernel.)
I can only find testing NUMA code and hardware as a reason to have
emulation enabled on a non-NUMA system?
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