On 08.07.2015 23:17, Tom Herbert wrote:
On Wed, Jul 8, 2015 at 10:49 AM, Oliver Hartkopp <socket...@hartkopp.net> wrote:
(..)
When receiving CAN frames from a specific CAN network interface (e.g. can0)
the frames are sporadically out-of-order on SMP systems like my Core i7 laptop
with 4 CPUs. This out-of-order reception kills reliable communication e.g. for
CAN transport protocols.
First approach was to set the smp_affinity for the USB adapter on irq 28 with:
(..)
Next idea was to use RPS after reading Documentation/networking/scaling.txt
(..)
My two questions:
1. Is there any better solution to meet the described requirements?
I would suggest that you look into how there are OOO packets in the
first place. Even if the interrupts is allowed to happen on different
CPUs by sm_affinity, NAPI execution should be serialized for the
device so that OOO shouldn't happen. The result of your RPS setting
should be all packets go to the same queue, this shouldn't normally
affect the ordering. Looking at drivers/net/can there are apparently
several variants of the driver. Do you know which one you're running?
I have two CAN hardware interfaces I can test together with a SMP system:
1. PCAN-USB using the driver at drivers/net/can/usb/peak_usb/
2. PCAN Compact PCIe using drivers/net/can/sja1000/(peak_pci.c / sja1000.c)
Both drivers do not use NAPI. The just follow the way
interrupt -> alloc_skb() -> fill skb -> netif_rx(skb)
I'm usually testing with the USB adapters as the PCIe setup is not very handy.
Best regards,
Oliver
2. If not: How can enable this RPS solution by default for CAN interfaces?
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