Yes the wakeup happens deep inside the critical section and if the process
is running on another CPU it could race to the lock.
Hmm, i suppose the wakeup could be moved out, but it would need some
restructuring of the code. Also to be safe the code would still need
to at least hold a reference count of the sock during the wakeup, and
when that is released then you have another cache line to bounce,
which might not be any better than the lock. So it might not be
actually worth it.
I suppose the socket release could be at least partially protected with
RCU against this case so that could be done without a reference count, but
it might be tricky to get this right.
Again still not sure it's worth handling this.
Based on my experiments thusfar I'd have to agree/accept (I wasn't
certain to begin with - hence the post in the first place :) but I do
need/want to see what happens with a single-stream through a 10G NIC -
on the receive side at least with a 1500 byte MTU.
I was using the burst-mode aggregate RR over the 1G NICs to get the CPU
util up without need for considerable bandwidth, since the system
handled 8 TCP_STREAM tests across the 8 NICs without working-up a sweat.
I suppose I could instead chop the MTU on the 1G NICs and use that to
increase the CPU util on the receive side.
rick
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