On Thu, 23 Jan 2020, Gleb Smirnoff wrote:
On Thu, Jan 23, 2020 at 05:09:14PM -1000, Jeff Roberson wrote:
J> While we don't have a policy strictly requiring reviews it is the norm to
J> have substantial changes socialized and reviewed. I appreciate the work
J> that you are doing but it likely should've been discussed somewhere
J> more publicly. I apologized if I missed it but I don't see reference to
J> anything.
That was https://reviews.freebsd.org/D23242
Ok thank you. Can you tag commits so people can see the discussion? Was
it in one I missed? When I'm committing a long patch series I include the
link in all of them.
Ryan, are you subscribed to @networking?
J> Architecturally I am more concerned with the coarseness of net_epoch and
J> the duration of hold becoming a resource utilization problem in high
J> turn-over workloads. Like short connection tcp. Has anyone done
J> substantial testing here? epoch as it is today will hold every free
J> callback for a minimum of several clock ticks and a maximum of 2x the
J> duration of the longest epoch section time. With preemption, etc. this
J> could be 100s of ms of PCBs held.
We also are concerned about that theoretically. Haven't yet seen effect
in practice, but our sessions are mostly longer living. First we have the
tunable to limit batching. Second, there are some ideas on how to improve
the garbage collector performance if it becomes an issue.
I am often surprised at how much cpu time I see on linux spent in RCU free
processing. Many of these things are written in such a way that
everything is cache cold by the time you swing back around. So the
callout walk is a giant cold linked list.
Thanks,
Jeff
--
Gleb Smirnoff
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