Re: Best way to set kernel thread affinity for handling a socket?

On Wed, Aug 22, 2012 at 9:21 AM, Ben Hutchings
[off-list ref] wrote:

With RFS we try to do the reverse: move the packets to match the socket
user.   But it's not (yet) turned on by default.  See
Documentation/networking/scaling.txt

Fair enough.  However I think at least in this case it sounds like extra
overhead: it should be easy for us to do everything on the CPU where
the packets are being received.

quoted

I'm thinking about this in the context of the kernel's iSCSI target
code (drivers/target/iscsi), which creates threads to handle each
iSCSI connection and sets their CPU affinity pretty much randomly
(well, based on some "thread id", cf iscsit_thread_get_cpumask()).

Why set the affinity at all?

It's quite possible that, like a lot of other drivers/target code, this
doesn't actually make any sense and the right answer is to rip it
out completely.

Is the affinity due to waking up from a network receive event
enough to keep the threads local to the right CPU?

 - R.