svn commit: r357051 - head/sys/dev/bge
Jeff Roberson
jroberson at jroberson.net
Fri Jan 24 04:18:27 UTC 2020
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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