On Thu, 10 Aug 2017 00:29:19 +0200 Francois Romieu <rom...@fr.zoreil.com> wrote:
> Murali Karicheri <m-kariche...@ti.com> : > [...] > > The internal memory or FIFO can store only up to 3 MTU sized packets. So > > that has to > > be processed before PRU gets another packets to send to CPU. So per above, > > it is not ideal to run NAPI for this scenario, right? Also for NetCP we use > > about 128 descriptors with MTU size buffers to handle 1Gbps Ethernet link. > > Based on that roughly we would need at least 10-12 buffers in the FIFO. > > > > Currently we have a NAPI implementation in use that gives throughput of > > 95Mbps for > > MTU sized packets, but our UDP iperf tests shows less than 1% packet loss > > for an > > offered traffic of 95Mbps with MTU sized packets. This is not good for > > industrial > > network using HSR/PRP protocol for network redundancy. We need to have zero > > packet > > loss for MTU sized packets at 95Mbps throughput. That is the problem > > description. > > Imvho you should instrument the kernel to figure where the excess latency that > prevents NAPI processing to take place within 125 us of physical packet > reception > comes from. > > > As an experiment, I have moved the packet processing to irq handler to see > > if we > > can take advantage of CPU cycle to processing the packet instead of NAPI > > and to check if the firmware encounters buffer overflow. The result is > > positive > > with no buffer overflow seen at the firmware and no packet loss in the > > iperf test. > > But we want to do more testing as an experiment and ran into a uart console > > locks > > up after running traffic for about 2 minutes. So I tried enabling the DEBUG > > HACK > > options to get some clue on what is happening and ran into the trace I > > shared > > earlier. So what function can I use to allocate SKB from interrupt handler > > ? > > Is your design also so tight on memory that you can't even refill your own > software skb pool from some non-irq context then only swap buffers in the > irq handler ? > The current best practice in network drivers is to receive into an allocated page, then create skb meta data with build_skb() in the NAPI poll routine.
