Fri, Jun 17, 2016 at 03:48:35PM CEST, dsa@cumulusnetworks.com wrote:
On 6/17/16 2:24 AM, Jiri Pirko wrote:
quoted
The problem we try to handle is different, it's about offloaded
forwarded packets which are not seen by kernel. Let me try to draw it :)
port1 port2 (HW stats are counted here)
\ /
\ /
\ /
--(A)---- ASIC --(B)--
|
(C)
|
CPU (SW stats are counted here)
Now we have couple of flows for TX and RX (direction does not matter here):
1) port1->A->ASIC->C->CPU
For this flow, HW and SW stats are equal.
2) port1->A->ASIC->C->CPU->C->ASIC->B->port2
For this flow, HW and SW stats are equal.
3) port1->A->ASIC->B->port2
For this flow, SW stats are 0.
The purpose of this patchset is to provide facility for user to
find out the difference between flows 1+2 and 3. In other words, user
will be able to see the statistics for his slow-path (through kernel).
Also, as a default the accumulated stats (HW) will be exposed to user
so the userspace apps can react properly.
You no longer agree with this discussion?
http://comments.gmane.org/gmane.linux.network/346740
Essentially netdevice stats show counters for packets punted to the cpu and
ethool -S shows h/w stats. This patch set seems to invert that.
That is problematic. Existing apps depend on rtnetlink stats. But if we
don't count offloaded forwarded packets, the apps don't see anything.
Therefore I believe that this patchset approach is better. The existing
apps continue to work and future apps can use newly introduces sw_stats
to query slowpath traffic. Makes sense to me.