> On a system that has SNC disabled the function reports both "node_cpus"
> and "cache_cpus" equal to 56. In this case snc_ways() returns "2". It is
> the same on a system with SNC enabled that reports the previously mentioned
> variables to be different by a factor of two (36 and 72).
> Is it possible for node_cpus and cache_cpus to not be multiples of each
> other? (as in for example cache_cpus being 10 and node_cpus being 21?).
> If not I'd suggest using "==" instead of ">=".
Some CPUs may be offline when the test is run. E.g. with one CPU offline on SNC
node 0, you'd see node_cpus = 35 and cache_cpus = 71. But with one CPU offline
on node 1, you'd have node_cpus = 36, cache_cpus = 71.
> If yes then I guess something like this could work? :
+ if (node_cpus >= cache_cpus)
+ return 1;
+ else if (2 * node_cpus >= cache_cpus)
+ return 2;
+ else if (4 * node_cpus >= cache_cpus)
+ return 4;
This returns "4" for the 36 71 case. But should still be "2".
>> PS. I did my tests on two Intel Ice Lakes.
Perhaps easier to play with the algorithm in user code?
#include <stdio.h>
#include <stdlib.h>
static int snc(int node_cpus, int cache_cpus)
{
if (node_cpus >= cache_cpus)
return 1;
else if (2 * node_cpus >= cache_cpus)
return 2;
else if (4 * node_cpus >= cache_cpus)
return 4;
return -1;
}
int main(int argc, char **argv)
{
printf("%d\n", snc(atoi(argv[1]), atoi(argv[2])));
return 0;
}
N.B. it's probably not possible to handle the case where somebody took ALL the CPUs in SNC
node 1 offline (or SNC nodes 1,2,3 for the SNC 4 case).
I think it reasonable that the code handle some simple "small number of CPUs offline" cases.
But don't worry too much about cases where the user has done something extreme.
-Tony
