+##
+# @ThreadContextProperties:
+#
+# Properties for thread context objects.
+#
+# @cpu-affinity: the CPU affinity for all threads created in the thread
+# context (default: QEMU main thread affinity)
+#
+# Since: 7.2
+##
+{ 'struct': 'ThreadContextProperties',
+ 'data': { '*cpu-affinity': ['uint16'] } }
I understand this is a list of affinities. What I poor ignorant me
doesn't understand is the meaning of the list index. Or in other words,
the list maps some range [0:N] to affinities, but what are the numbers
being mapped there?
Assume you have 8 physical CPUs.
$ lscpu
...
NUMA:
NUMA node(s): 1
NUMA node0 CPU(s): 0-7
...
You will provide the CPU IDs here, for example as in patch #7 example:
qemu-system-x86_64 -m 1G \
-object thread-context,id=tc1,cpu-affinity=3-4 \
-object
memory-backend-ram,id=pc.ram,size=1G,prealloc=on,prealloc-threads=2,prealloc-context=tc1
\
-machine memory-backend=pc.ram \
-S -monitor stdio -sandbox enable=on,resourcecontrol=deny
Details about CPU affinities in general can be found in the man page of taskset:
https://man7.org/linux/man-pages/man1/taskset.1.html
Is @cpu-affinity a set of CPU numbers?
Yes! For now I added to the description:
...
General information about CPU affinities can be found in the man page of
taskset:
CPU affinity is a scheduler property that "bonds" a process to a given
set of CPUs on the system. The Linux scheduler will honor the given CPU
affinity and the process will not run on any other CPUs.
...
A simple QEMU example to set the CPU affinity to CPU 0,1,6,7 would be:
qemu-system-x86_64 -S \
-object thread-context,id=tc1,cpu-affinity=0-1,cpu-affinity=6-7
And we can query it via HMP/QMP:
(qemu) qom-get tc1 cpu-affinity
[
0,
1,
6,
7
]
But note that due to dynamic library loading this example will not work
before we actually make use of thread_context_create_thread() in QEMU
code, because the type will otherwise not get registered.
Please let me know how I can further clarify this, that would help, thanks!
What happens when you try to create a thread context object with CPU
affinities on a host system that doesn't support CPU affinities?
qemu_thread_set_affinity() will fail and setting the attribute will result
in a "Setting CPU affinity failed".
Thanks!
--
Thanks,
David / dhildenb
