Hi Rafael,
Rafael Vanoni wrote:
Hi everyone,
I was wondering if someone could help me with a doubt I ran into while
reading Solaris Internals.
On p802, chapter 16.4, last paragraph, it says that real-time threads
don't benefit from scheduling affinity because the implementation is
POSIX conformant.
I'm not very familiar with what POSIX imposes on scheduling, could
someone explain that to me?
When threads in the RT scheduling class become runnable, they are placed
on a per CPU partition run queue, that
all CPUs in the partition may pull from. This run queue is called the
"kp" queue, and is embedded in the cpu partition structure
(See definition of CPU partitions on page 165). Even though all CPUs in
the partition may take/run the thread sitting on the kp queue,
setkpdq() (which is the function that enqueues the thread) will actually
try to designate a CPU in the thread's home lgroup as the "chosen" CPU
(since it uses NUMA aware disp_lowpri_cpu() to select one), which it
will try to preempt a lower priority thread running there. So threads in
the RT scheduling class probably will still exhibit affinity for the
CPUs in their home lgroup...but depending on the number of other CPUs in
the partition, how idle those CPUs, etc...the degree of affinity
exhibited may vary.
-Eric
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