> -----Original Message----- > From: Jakub Kicinski <kuba@xxxxxxxxxx> > Sent: Monday, August 14, 2023 9:00 PM > To: Pandey, Radhey Shyam <radhey.shyam.pandey@xxxxxxx> > Cc: vkoul@xxxxxxxxxx; robh+dt@xxxxxxxxxx; > krzysztof.kozlowski+dt@xxxxxxxxxx; conor+dt@xxxxxxxxxx; Simek, Michal > <michal.simek@xxxxxxx>; davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; > pabeni@xxxxxxxxxx; linux@xxxxxxxxxxxxxxx; dmaengine@xxxxxxxxxxxxxxx; > devicetree@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; git (AMD-Xilinx) > <git@xxxxxxx> > Subject: Re: [PATCH net-next v5 10/10] net: axienet: Introduce dmaengine > support > > On Sat, 12 Aug 2023 15:27:19 +0000 Pandey, Radhey Shyam wrote: > > > Drop on error, you're not stopping the queue correctly, just drop, return > OK > > > and avoid bugs. > > > > As I understand NETDEV_TX_OK returns means driver took care of packet. > > So inline with non-dmaengine xmit (axienet_start_xmit_legacy) should > > we stop the queue and return TX_BUSY? > > You should only return BUSY if there is no space. All other errors > should lead to drops, and increment of tx_error. Otherwise problem > with handling a single packet may stall the NIC forever. > It is somewhat confusing that we return TX_OK in that case but it > is what it is. > > > > Why create a cache ? > > > Isn't it cleaner to create a fake ring buffer of sgl? Most packets will not > have > > > MAX_SKB_FRAGS of memory. On a ring buffer you can use only as many > sg > > > entries as the packet requires. Also no need to alloc/free. > > > > The kmem_cache is used with intent to use slab cache interface and > > make use of reusing objects in the kernel. slab cache maintains a > > cache of objects. When we free an object, instead of > > deallocating it, it give it back to the cache. Next time, if we > > want to create a new object, slab cache gives us one object from the > > slab cache. > > > > If we maintain custom circular buffer (struct circ_buf) ring buffer > > we have to create two such ring buffers one for TX and other for RX. > > For multichannel this will multiply to * no of queues. Also we have to > > ensure proper occupancy checks and head/tail pointer updates. > > > > With kmem_cache pool we are offloading queue maintenance ops to > > framework with a benefit of optimized alloc/dealloc. Let me know if it > > looks functionally fine and can retain it for this baseline dmaengine > > support version? > > The kmemcache is not the worst possible option but note that the > objects you're allocating (with zeroing) are 512+ bytes. That's > pretty large, when most packets will not have full 16 fragments. > Ring buffer would allow to better match the allocation size to > the packets. Not to mention that it can be done fully locklessly. I modified the implementation to use a circular ring buffer for TX and RX. It seems to be working in initial testing and now running perf tests. Just had one question on when to submit v6 ? Wait till dmaengine patches([01/10-[07/10] is part of net-next? Or can I send it now also. Thanks, Radhey
