Hello VPP folks, I have several questions/comments on memif and libmemif.
1) I believe "mq[x].last_tail = 0" is missing from memif_init_regions_and_queues(). 2) I have a libmemif app connecting to two different memif sockets and I noticed that if my app fails to connect to the first socket it will not attempt the second. This is due to the error bailout in memif_control_fd_handler(), line 921. Is this behavior intended? 3) memif ring size 3a) I see both memif plugin and libmemif set the max ring size as: #define MEMIF_MAX_LOG2_RING_SIZE 14 However, src/plugins/memif/cli.c has the following check: if (ring_size > 32768) return clib_error_return (0, "maximum ring size is 32768"); Which is correct? For what it's worth, I modified the #define to allow a ring size of 32768 and it appeared to work, but I'm not certain there wasn't something bad (but non-fatal) happening behind the scenes. 3b) What is the source of the 32k limit? Is this a technical limit or a "you shouldn't need more than this" limit? 3c) What ring size was used for the benchmarks shown at KubeCon EU? (https://wiki.fd.io/view/File:Fdio-memif-at-kubecon-eu-180430.pptx) 4) Is it still true that libmemif cannot act as master? (https://lists.fd.io/g/vpp-dev/message/9408) 5) Suppose that after calling memif_buffer_alloc(), while populating the tx buffer, you decide you no longer want to transmit the buffer. How do you "give back" the tx buffer to the ring? 6) memif_refill_queue 6a) Debugging some performance issues in my libmemif app, I benchmarked memif_refill_queue() and found that with a headroom of 128 the function was taking almost 2600 clocks per call on average: libmemif_refill: 4971105 samples, 12799435227 clocks (avg: 2574) But with a headroom of 0, only 22 clocks per call on average: libmemif_refill: 4968243 samples, 111850110 clocks (avg: 22) Is this expected? 6b) How should memif_refill_queue() be used in a scenario where the received packets are processed at different times? For example, suppose I receive 16 packets from memif_rx_burst(), p0-p15. I want to hold on to p4, p9, p11 temporarily and process+transmit the others via memif_tx_burst(). There's no way to call memif_refill_queue() for just the 13 processed packets, correct? Would I need to make copies of p4, p9, p11 and then refill all 16? 7) Looking for more information on the memif_buffer_enqueue_tx() function. I see it used only in the zero-copy-slave example code. Is the combination of memif_buffer_enqueue_tx() + memif_tx_burst() the way to achieve zero-copy tx? If not, how/where should memif_buffer_enqueue_tx() be used? Is zero-copy only possible from slave->master? Thanks, Jeff
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