Andrew Morton wrote:
Shailabh Nagar <[EMAIL PROTECTED]> wrote:
+/*
+ * Per-task exit data sent from the kernel to user space
+ * is tagged by an id based on grouping of cpus.
+ *
+ * If userspace specifies a non-zero P as the nl_pid field of
+ * the sockaddr_nl structure while binding to a netlink socket,
+ * it will receive exit data from threads that exited on cpus in the range
+ *
+ * [(P-1)*Y, P*Y-1]
+ *
+ * where Y = TASKSTATS_CPUS_PER_SET
+ * i.e. if TASKSTATS_CPUS_PER_SET is 16,
+ * to listen to data from cpus 0..15, specify P=1
+ * for cpus 16..32, specify P=2 etc.
+ *
+ * To listen to data from all cpus, userspace should use P=0
+ */
+
+#define TASKSTATS_CPUS_PER_SET 16
The constant is unpleasant.
I was planning to make it configurable. But that would still not be as
flexible as below...
If we're going to abuse nl_pid then how about we design things so that
nl_pid is treated as two 16-bit words - one word is the start CPU and the
other word is the end cpu?
Or, if a 65536-CPU limit is too scary, make the bottom 8 bits of nl_pid be
the number of CPUS (ie: TASKSTATS_CPUS_PER_SET) and the top 24 bits is the
starting CPU.
<avoids mentioning nl_pad>
It'd be better to use a cpumask, of course..
All these options mean each listener gets to pick a "custom" range of
cpus to listen on,
rather than choose one of pre-defined ranges (even if the pre-defined
ranges can change
by a configurable TASKSTATS_CPUS_PER_SET). Which means the kernel side
has to
figure out which of the listeners cpu range includes the currently
exiting task's cpu. To do
this, we'll need a callback from the binding of the netlink socket (so
taskstats can maintain
the cpu -> nl_pid mappings at any exit).
The current genetlink interface doesn't have that kind of flexibility
(though it can be added
I'm sure).
Seems a bit involved if the primary aim is to restrict the number of
cpus that one listener
wants to listen, rather than be able to pick which ones.
A configurable range won't suffice ?
--Shailabh
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