问题
This question asks about ensuring two processes run on the same CPU. Using sched_setaffinity
I can limit a process to a number of logical CPUs, but how can I ensure that these are mapped to specific physical CPUs and threads?
I expect that the mapping would be:
0 - CPU 0 thread 0
1 - CPU 0 thread 1
2 - CPU 1 thread 0
3 - CPU 1 thread 1
etc...
where the number on the left is the relevant CPU used in sched_setaffinity
.
However, when I tried to test this, it appeared that this is not necessarily the case.
To test this, I used the CPUID
instruction, which returns the initial APIC ID of the current core in EBX
:
void print_cpu()
{
int cpuid_out;
__asm__(
"cpuid;"
: "=b"(cpuid_out)
: "a"(1)
:);
std::cout << "I am running on cpu " << std::hex << (cpuid_out >> 24) << std::dec << std::endl;
}
Then I looped over the bits in the cpu mask and set them one at a time so that the OS would migrate the process to each logical CPU in turn, and then I printed out the current CPU.
This is what I got:
cpu mask is 0
I am running on cpu 0
cpu mask is 1
I am running on cpu 4
cpu mask is 2
I am running on cpu 2
cpu mask is 3
I am running on cpu 6
cpu mask is 4
I am running on cpu 1
cpu mask is 5
I am running on cpu 5
cpu mask is 6
I am running on cpu 3
cpu mask is 7
I am running on cpu 7
assuming that the CPU assigns initial APIC IDs according to the scheme I listed above, it would seem that the cpu mask doesn't actually correspond to the physical core and thread.
How can I find the correct mapping of bits in the mask for sched_setaffinity
to physical cores?
回答1:
hwloc is a portable C library for discovering hardware/NUMA topology, and also binding processes/threads to particular cores. It has functions to discover physical/logical cores, and then bind a process/thread to it.
It also looks like it can also return a cpu_set_t
for use with sched_setaffinity()
, if you want to keep using that directly.
来源:https://stackoverflow.com/questions/9386229/how-can-i-ensure-that-a-process-runs-in-a-specific-physical-cpu-core-and-thread