Rusty Russell a écrit : > On Sat, 30 May 2009 12:41:00 am Eric Dumazet wrote: >> Rusty Russell a écrit : >>> DaveM points out that there are advantages to doing it generally (it's >>> more likely to be on same CPU than after xmit), and I couldn't find >>> any new starvation issues in simple benchmarking here. >> If really no starvations are possible at all, I really wonder why some >> guys added memory accounting to UDP flows. Maybe they dont run "simple >> benchmarks" but real apps ? :) > > Well, without any accounting at all you could use quite a lot of memory as > there are many places packets can be queued. > >> For TCP, I agree your patch is a huge benefit, since its paced by remote >> ACKS and window control > > I doubt that. There'll be some cache friendliness, but I'm not sure it'll be > measurable, let alone "huge". It's the win to drivers which don't have a > timely and batching tx free mechanism which I aim for. At 250.000 packets/second on a Gigabit link, this is huge, I can tell you. (250.000 incoming packets and 250.000 outgoing packets per second, 700 Mbit/s) According to this oprofile on CPU0 (dedicated to softirqs on one bnx2 eth adapter) We can see sock_wfree() being number 2 on the profile, because it touches three cache lines per socket and transmited packet in TX completion handler. Also, taking a reference on socket for each xmit packet in flight is very expensive, since it slows down receiver in __udp4_lib_lookup(). Several cpus are fighting for sk->refcnt cache line. CPU: Core 2, speed 3000.24 MHz (estimated) Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000 samples cum. samples % cum. % symbol name 21215 21215 11.8847 11.8847 bnx2_poll_work 17239 38454 9.6573 21.5420 sock_wfree << effect of udp memory accounting >> 14817 53271 8.3005 29.8425 __slab_free 14635 67906 8.1986 38.0411 __udp4_lib_lookup 11425 79331 6.4003 44.4414 __alloc_skb 9710 89041 5.4396 49.8810 __slab_alloc 8095 97136 4.5348 54.4158 __udp4_lib_rcv 7831 104967 4.3869 58.8027 sock_def_write_space 7586 112553 4.2497 63.0524 ip_rcv 7518 120071 4.2116 67.2640 skb_dma_unmap 6711 126782 3.7595 71.0235 netif_receive_skb 6272 133054 3.5136 74.5371 udp_queue_rcv_skb 5262 138316 2.9478 77.4849 skb_release_data 5023 143339 2.8139 80.2988 __kmalloc_track_caller 4070 147409 2.2800 82.5788 kmem_cache_alloc 3216 150625 1.8016 84.3804 ipt_do_table 2576 153201 1.4431 85.8235 skb_queue_tail _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
