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Date: Wed, 27 Jan 2016 18:50:27 -0800 From: Tom Herbert <tom@...bertland.com> To: Jesper Dangaard Brouer <brouer@...hat.com> Cc: John Fastabend <john.fastabend@...il.com>, "Michael S. Tsirkin" <mst@...hat.com>, David Miller <davem@...emloft.net>, Eric Dumazet <eric.dumazet@...il.com>, Or Gerlitz <gerlitz.or@...il.com>, Eric Dumazet <edumazet@...gle.com>, Linux Kernel Network Developers <netdev@...r.kernel.org>, Alexander Duyck <alexander.duyck@...il.com>, Alexei Starovoitov <alexei.starovoitov@...il.com>, Daniel Borkmann <borkmann@...earbox.net>, Marek Majkowski <marek@...udflare.com>, Hannes Frederic Sowa <hannes@...essinduktion.org>, Florian Westphal <fw@...len.de>, Paolo Abeni <pabeni@...hat.com>, John Fastabend <john.r.fastabend@...el.com>, Amir Vadai <amirva@...il.com>, Daniel Borkmann <daniel@...earbox.net>, Vladislav Yasevich <vyasevich@...il.com> Subject: Re: Bypass at packet-page level (Was: Optimizing instruction-cache, more packets at each stage) On Wed, Jan 27, 2016 at 12:47 PM, Jesper Dangaard Brouer <brouer@...hat.com> wrote: > On Mon, 25 Jan 2016 23:10:16 +0100 > Jesper Dangaard Brouer <brouer@...hat.com> wrote: > >> On Mon, 25 Jan 2016 09:50:16 -0800 John Fastabend <john.fastabend@...il.com> wrote: >> >> > On 16-01-25 09:09 AM, Tom Herbert wrote: >> > > On Mon, Jan 25, 2016 at 5:15 AM, Jesper Dangaard Brouer >> > > <brouer@...hat.com> wrote: >> > >> >> [...] >> > >> >> > >> There are two ideas, getting mixed up here. (1) bundling from the >> > >> RX-ring, (2) allowing to pick up the "packet-page" directly. >> > >> >> > >> Bundling (1) is something that seems natural, and which help us >> > >> amortize the cost between layers (and utilizes icache better). Lets >> > >> keep that in another thread. >> > >> >> > >> This (2) direct forward of "packet-pages" is a fairly extreme idea, >> > >> BUT it have the potential of being an new integration point for >> > >> "selective" bypass-solutions and bringing RAW/af_packet (RX) up-to >> > >> speed with bypass-solutions. >> > >> [...] >> > >> > Jesper, at least for you (2) case what are we missing with the >> > bifurcated/queue splitting work? Are you really after systems >> > without SR-IOV support or are you trying to get this on the order >> > of queues instead of VFs. >> >> I'm not saying something is missing for bifurcated/queue splitting work. >> I'm not trying to work-around SR-IOV. >> >> This an extreme idea, which I got while looking at the lowest RX layer. >> >> >> Before working any further on this idea/path, I need/want to evaluate >> if it makes sense from a performance point of view. I need to evaluate >> if "pulling" out these "packet-pages" is fast enough to compete with >> DPDK/netmap. Else it makes no sense to work on this path. >> >> As a first step to evaluate this lowest RX layer, I'm simply hacking >> the drivers (ixgbe and mlx5) to drop/discard packets within-the-driver. >> For now, simply replacing napi_gro_receive() with dev_kfree_skb(), and >> measuring the "RX-drop" performance. >> >> Next step was to avoid the skb alloc+free calls, but doing so is more >> complicated that I first anticipated, as the SKB is tied in fairly >> heavily. Thus, right now I'm instead hooking in my bulk alloc+free >> API, as that will remove/mitigate most of the overhead of the >> kmem_cache/slab-allocators. > > I've tried to deduct that kind of speeds we can achieve, at this lowest > RX layer. By in the mlx5/100G driver drop packets directly in the driver. > Just replacing replacing napi_gro_receive() with dev_kfree_skb(), was > fairly depressing, showing only 6.2Mpps (6253970 pps => 159.9 ns) (single core). > > Looking at the perf report showed major cache-miss in eth_type_trans(29%/47ns). > > And driver is hitting the SLUB slowpath quite badly (because it > prealloc SKBs and binds to RX ring, usually this test case would hits > SLUB "recycle" fastpath): > > Group-report: kmem_cache/SLUB allocator functions :: > 5.00 % ~= 8.0 ns <= __slab_free > 4.91 % ~= 7.9 ns <= cmpxchg_double_slab.isra.65 > 4.22 % ~= 6.7 ns <= kmem_cache_alloc > 1.68 % ~= 2.7 ns <= kmem_cache_free > 1.10 % ~= 1.8 ns <= ___slab_alloc > 0.93 % ~= 1.5 ns <= __cmpxchg_double_slab.isra.54 > 0.65 % ~= 1.0 ns <= __slab_alloc.isra.74 > 0.26 % ~= 0.4 ns <= put_cpu_partial > Sum: 18.75 % => calc: 30.0 ns (sum: 30.0 ns) => Total: 159.9 ns > > To get around the cache-miss in eth_type_trans(), I created a > "icache-loop" in mlx5e_poll_rx_cq() and pull all RX-ring packets "out", > before calling eth_type_trans(), reducing cost to 2.45%. > > To mitigate the SLUB slowpath, I used my slab + SKB-napi bulk API . And > also tuned SLUB (with slub_nomerge slub_min_objects=128) to get bigger > slab-pages, thus bigger bulk opportunities. > > This helped a lot, I can now drop 12Mpps (12,088,767 => 82.7 ns). > > Group-report: kmem_cache/SLUB allocator functions :: > 4.99 % ~= 4.1 ns <= kmem_cache_alloc_bulk > 2.87 % ~= 2.4 ns <= kmem_cache_free_bulk > 0.24 % ~= 0.2 ns <= ___slab_alloc > 0.23 % ~= 0.2 ns <= __slab_free > 0.21 % ~= 0.2 ns <= __cmpxchg_double_slab.isra.54 > 0.17 % ~= 0.1 ns <= cmpxchg_double_slab.isra.65 > 0.07 % ~= 0.1 ns <= put_cpu_partial > 0.04 % ~= 0.0 ns <= unfreeze_partials.isra.71 > 0.03 % ~= 0.0 ns <= get_partial_node.isra.72 > Sum: 8.85 % => calc: 7.3 ns (sum: 7.3 ns) => Total: 82.7 ns > > Full perf report output below signature, is from optimized case. > > SKB related cost is 22.9 ns. However 51.7% (11.84ns) cost originates > from memset of the SKB. > > Group-report: related to pattern "skb" :: > 17.92 % ~= 14.8 ns <= __napi_alloc_skb <== 80% memset(0) / rep stos > 3.29 % ~= 2.7 ns <= skb_release_data > 2.20 % ~= 1.8 ns <= napi_consume_skb > 1.86 % ~= 1.5 ns <= skb_release_head_state > 1.20 % ~= 1.0 ns <= skb_put > 1.14 % ~= 0.9 ns <= skb_release_all > 0.02 % ~= 0.0 ns <= __kfree_skb_flush > Sum: 27.63 % => calc: 22.9 ns (sum: 22.9 ns) => Total: 82.7 ns > > Doing a crude extrapolation, 82.7 ns subtract, SLUB (7.3 ns) and SKB > (22.9 ns) related => 52.5 ns -> extrapolate 19 Mpps would be the > maximum speed we can pull off packet-pages from the RX ring. > > I don't know if 19Mpps (52.5 ns "overhead") is fast enough, to compete > with just mapping a RX HW queue/ring to netmap or via SR-IOV to DPDK(?) > > But it was interesting to see how the lowest RX layer performs... Cool stuff! Looking at the typical driver receive path, I'm wonder if we should beak netif_receive_skb (napi_gro_receive) into two parts. One utility function to create a list of received skb's and prefetch the data called as ring is processed, the other one to give the list to the stack (e.g. netif_receive_skbs) and defer eth_type_trans as long as possible. Is something like this what you are contemplating? Tom > -- > Best regards, > Jesper Dangaard Brouer > MSc.CS, Principal Kernel Engineer at Red Hat > Author of http://www.iptv-analyzer.org > LinkedIn: http://www.linkedin.com/in/brouer > > > Perf-report script: > * https://github.com/netoptimizer/network-testing/blob/master/bin/perf_report_pps_stats.pl > > Report: ALL functions :: > 19.71 % ~= 16.3 ns <= mlx5e_poll_rx_cq > 17.92 % ~= 14.8 ns <= __napi_alloc_skb > 9.54 % ~= 7.9 ns <= __free_page_frag > 7.16 % ~= 5.9 ns <= mlx5e_get_cqe > 6.37 % ~= 5.3 ns <= mlx5e_post_rx_wqes > 4.99 % ~= 4.1 ns <= kmem_cache_alloc_bulk > 3.70 % ~= 3.1 ns <= __alloc_page_frag > 3.29 % ~= 2.7 ns <= skb_release_data > 2.87 % ~= 2.4 ns <= kmem_cache_free_bulk > 2.45 % ~= 2.0 ns <= eth_type_trans > 2.43 % ~= 2.0 ns <= get_page_from_freelist > 2.36 % ~= 2.0 ns <= swiotlb_map_page > 2.20 % ~= 1.8 ns <= napi_consume_skb > 1.86 % ~= 1.5 ns <= skb_release_head_state > 1.25 % ~= 1.0 ns <= free_pages_prepare > 1.20 % ~= 1.0 ns <= skb_put > 1.14 % ~= 0.9 ns <= skb_release_all > 0.77 % ~= 0.6 ns <= __free_pages_ok > 0.59 % ~= 0.5 ns <= get_pfnblock_flags_mask > 0.59 % ~= 0.5 ns <= swiotlb_dma_mapping_error > 0.59 % ~= 0.5 ns <= unmap_single > 0.58 % ~= 0.5 ns <= _raw_spin_lock_irqsave > 0.57 % ~= 0.5 ns <= free_one_page > 0.56 % ~= 0.5 ns <= swiotlb_unmap_page > 0.52 % ~= 0.4 ns <= _raw_spin_lock > 0.46 % ~= 0.4 ns <= __mod_zone_page_state > 0.36 % ~= 0.3 ns <= __rmqueue > 0.36 % ~= 0.3 ns <= net_rx_action > 0.34 % ~= 0.3 ns <= __alloc_pages_nodemask > 0.31 % ~= 0.3 ns <= __zone_watermark_ok > 0.27 % ~= 0.2 ns <= mlx5e_napi_poll > 0.24 % ~= 0.2 ns <= ___slab_alloc > 0.23 % ~= 0.2 ns <= __slab_free > 0.22 % ~= 0.2 ns <= __list_del_entry > 0.21 % ~= 0.2 ns <= __cmpxchg_double_slab.isra.54 > 0.21 % ~= 0.2 ns <= next_zones_zonelist > 0.20 % ~= 0.2 ns <= __list_add > 0.17 % ~= 0.1 ns <= __do_softirq > 0.17 % ~= 0.1 ns <= cmpxchg_double_slab.isra.65 > 0.16 % ~= 0.1 ns <= __inc_zone_state > 0.12 % ~= 0.1 ns <= _raw_spin_unlock > 0.12 % ~= 0.1 ns <= zone_statistics > (Percent limit(0.1%) stop at "mlx5e_poll_tx_cq") > Sum: 99.45 % => calc: 82.3 ns (sum: 82.3 ns) => Total: 82.7 ns > > Group-report: related to pattern "eth_type_trans|mlx5|ixgbe|__iowrite64_copy" :: > (Driver related) > 19.71 % ~= 16.3 ns <= mlx5e_poll_rx_cq > 7.16 % ~= 5.9 ns <= mlx5e_get_cqe > 6.37 % ~= 5.3 ns <= mlx5e_post_rx_wqes > 2.45 % ~= 2.0 ns <= eth_type_trans > 0.27 % ~= 0.2 ns <= mlx5e_napi_poll > 0.09 % ~= 0.1 ns <= mlx5e_poll_tx_cq > Sum: 36.05 % => calc: 29.8 ns (sum: 29.8 ns) => Total: 82.7 ns > > Group-report: DMA functions :: > 2.36 % ~= 2.0 ns <= swiotlb_map_page > 0.59 % ~= 0.5 ns <= unmap_single > 0.59 % ~= 0.5 ns <= swiotlb_dma_mapping_error > 0.56 % ~= 0.5 ns <= swiotlb_unmap_page > Sum: 4.10 % => calc: 3.4 ns (sum: 3.4 ns) => Total: 82.7 ns > > Group-report: page_frag_cache functions :: > 9.54 % ~= 7.9 ns <= __free_page_frag > 3.70 % ~= 3.1 ns <= __alloc_page_frag > 2.43 % ~= 2.0 ns <= get_page_from_freelist > 1.25 % ~= 1.0 ns <= free_pages_prepare > 0.77 % ~= 0.6 ns <= __free_pages_ok > 0.59 % ~= 0.5 ns <= get_pfnblock_flags_mask > 0.57 % ~= 0.5 ns <= free_one_page > 0.46 % ~= 0.4 ns <= __mod_zone_page_state > 0.36 % ~= 0.3 ns <= __rmqueue > 0.34 % ~= 0.3 ns <= __alloc_pages_nodemask > 0.31 % ~= 0.3 ns <= __zone_watermark_ok > 0.21 % ~= 0.2 ns <= next_zones_zonelist > 0.16 % ~= 0.1 ns <= __inc_zone_state > 0.12 % ~= 0.1 ns <= zone_statistics > 0.02 % ~= 0.0 ns <= mod_zone_page_state > Sum: 20.83 % => calc: 17.2 ns (sum: 17.2 ns) => Total: 82.7 ns > > Group-report: kmem_cache/SLUB allocator functions :: > 4.99 % ~= 4.1 ns <= kmem_cache_alloc_bulk > 2.87 % ~= 2.4 ns <= kmem_cache_free_bulk > 0.24 % ~= 0.2 ns <= ___slab_alloc > 0.23 % ~= 0.2 ns <= __slab_free > 0.21 % ~= 0.2 ns <= __cmpxchg_double_slab.isra.54 > 0.17 % ~= 0.1 ns <= cmpxchg_double_slab.isra.65 > 0.07 % ~= 0.1 ns <= put_cpu_partial > 0.04 % ~= 0.0 ns <= unfreeze_partials.isra.71 > 0.03 % ~= 0.0 ns <= get_partial_node.isra.72 > Sum: 8.85 % => calc: 7.3 ns (sum: 7.3 ns) => Total: 82.7 ns > > Group-report: related to pattern "skb" :: > 17.92 % ~= 14.8 ns <= __napi_alloc_skb <== 80% memset(0) / rep stos > 3.29 % ~= 2.7 ns <= skb_release_data > 2.20 % ~= 1.8 ns <= napi_consume_skb > 1.86 % ~= 1.5 ns <= skb_release_head_state > 1.20 % ~= 1.0 ns <= skb_put > 1.14 % ~= 0.9 ns <= skb_release_all > 0.02 % ~= 0.0 ns <= __kfree_skb_flush > Sum: 27.63 % => calc: 22.9 ns (sum: 22.9 ns) => Total: 82.7 ns > > Group-report: Core network-stack functions :: > 0.36 % ~= 0.3 ns <= net_rx_action > 0.17 % ~= 0.1 ns <= __do_softirq > 0.02 % ~= 0.0 ns <= __raise_softirq_irqoff > 0.01 % ~= 0.0 ns <= run_ksoftirqd > 0.00 % ~= 0.0 ns <= run_timer_softirq > 0.00 % ~= 0.0 ns <= ksoftirqd_should_run > 0.00 % ~= 0.0 ns <= raise_softirq > Sum: 0.56 % => calc: 0.5 ns (sum: 0.5 ns) => Total: 82.7 ns > > Group-report: GRO network-stack functions :: > Sum: 0.00 % => calc: 0.0 ns (sum: 0.0 ns) => Total: 82.7 ns > > Group-report: related to pattern "spin_.*lock|mutex" :: > 0.58 % ~= 0.5 ns <= _raw_spin_lock_irqsave > 0.52 % ~= 0.4 ns <= _raw_spin_lock > 0.12 % ~= 0.1 ns <= _raw_spin_unlock > 0.01 % ~= 0.0 ns <= _raw_spin_unlock_irqrestore > 0.00 % ~= 0.0 ns <= __mutex_lock_slowpath > 0.00 % ~= 0.0 ns <= _raw_spin_lock_irq > Sum: 1.23 % => calc: 1.0 ns (sum: 1.0 ns) => Total: 82.7 ns > > Negative Report: functions NOT included in group reports:: > 0.22 % ~= 0.2 ns <= __list_del_entry > 0.20 % ~= 0.2 ns <= __list_add > 0.07 % ~= 0.1 ns <= list_del > 0.05 % ~= 0.0 ns <= native_sched_clock > 0.04 % ~= 0.0 ns <= irqtime_account_irq > 0.02 % ~= 0.0 ns <= rcu_bh_qs > 0.01 % ~= 0.0 ns <= task_tick_fair > 0.01 % ~= 0.0 ns <= net_rps_action_and_irq_enable.isra.112 > 0.01 % ~= 0.0 ns <= perf_event_task_tick > 0.01 % ~= 0.0 ns <= apic_timer_interrupt > 0.01 % ~= 0.0 ns <= lapic_next_deadline > 0.01 % ~= 0.0 ns <= rcu_check_callbacks > 0.01 % ~= 0.0 ns <= smpboot_thread_fn > 0.01 % ~= 0.0 ns <= irqtime_account_process_tick.isra.3 > 0.00 % ~= 0.0 ns <= intel_bts_enable_local > 0.00 % ~= 0.0 ns <= kthread_should_park > 0.00 % ~= 0.0 ns <= native_apic_mem_write > 0.00 % ~= 0.0 ns <= hrtimer_forward > 0.00 % ~= 0.0 ns <= get_work_pool > 0.00 % ~= 0.0 ns <= cpu_startup_entry > 0.00 % ~= 0.0 ns <= acct_account_cputime > 0.00 % ~= 0.0 ns <= set_next_entity > 0.00 % ~= 0.0 ns <= worker_thread > 0.00 % ~= 0.0 ns <= dbs_timer_handler > 0.00 % ~= 0.0 ns <= delay_tsc > 0.00 % ~= 0.0 ns <= idle_cpu > 0.00 % ~= 0.0 ns <= timerqueue_add > 0.00 % ~= 0.0 ns <= hrtimer_interrupt > 0.00 % ~= 0.0 ns <= dbs_work_handler > 0.00 % ~= 0.0 ns <= dequeue_entity > 0.00 % ~= 0.0 ns <= update_cfs_shares > 0.00 % ~= 0.0 ns <= update_fast_timekeeper > 0.00 % ~= 0.0 ns <= smp_trace_apic_timer_interrupt > 0.00 % ~= 0.0 ns <= __update_cpu_load > 0.00 % ~= 0.0 ns <= cpu_needs_another_gp > 0.00 % ~= 0.0 ns <= ret_from_intr > 0.00 % ~= 0.0 ns <= __intel_pmu_enable_all > 0.00 % ~= 0.0 ns <= trigger_load_balance > 0.00 % ~= 0.0 ns <= __schedule > 0.00 % ~= 0.0 ns <= nsecs_to_jiffies64 > 0.00 % ~= 0.0 ns <= account_entity_dequeue > 0.00 % ~= 0.0 ns <= worker_enter_idle > 0.00 % ~= 0.0 ns <= __hrtimer_get_next_event > 0.00 % ~= 0.0 ns <= rcu_irq_exit > 0.00 % ~= 0.0 ns <= rb_erase > 0.00 % ~= 0.0 ns <= __intel_pmu_disable_all > 0.00 % ~= 0.0 ns <= tick_sched_do_timer > 0.00 % ~= 0.0 ns <= cpuacct_account_field > 0.00 % ~= 0.0 ns <= update_wall_time > 0.00 % ~= 0.0 ns <= notifier_call_chain > 0.00 % ~= 0.0 ns <= timekeeping_update > 0.00 % ~= 0.0 ns <= ktime_get_update_offsets_now > 0.00 % ~= 0.0 ns <= rb_next > 0.00 % ~= 0.0 ns <= rcu_all_qs > 0.00 % ~= 0.0 ns <= x86_pmu_disable > 0.00 % ~= 0.0 ns <= _cond_resched > 0.00 % ~= 0.0 ns <= __rcu_read_lock > 0.00 % ~= 0.0 ns <= __local_bh_enable > 0.00 % ~= 0.0 ns <= update_cpu_load_active > 0.00 % ~= 0.0 ns <= x86_pmu_enable > 0.00 % ~= 0.0 ns <= insert_work > 0.00 % ~= 0.0 ns <= ktime_get > 0.00 % ~= 0.0 ns <= __usecs_to_jiffies > 0.00 % ~= 0.0 ns <= __acct_update_integrals > 0.00 % ~= 0.0 ns <= scheduler_tick > 0.00 % ~= 0.0 ns <= update_vsyscall > 0.00 % ~= 0.0 ns <= memcpy_erms > 0.00 % ~= 0.0 ns <= get_cpu_idle_time_us > 0.00 % ~= 0.0 ns <= sched_clock_cpu > 0.00 % ~= 0.0 ns <= tick_do_update_jiffies64 > 0.00 % ~= 0.0 ns <= hrtimer_active > 0.00 % ~= 0.0 ns <= profile_tick > 0.00 % ~= 0.0 ns <= __hrtimer_run_queues > 0.00 % ~= 0.0 ns <= kthread_should_stop > 0.00 % ~= 0.0 ns <= run_posix_cpu_timers > 0.00 % ~= 0.0 ns <= read_tsc > 0.00 % ~= 0.0 ns <= __remove_hrtimer > 0.00 % ~= 0.0 ns <= calc_global_load_tick > 0.00 % ~= 0.0 ns <= hrtimer_run_queues > 0.00 % ~= 0.0 ns <= irq_work_tick > 0.00 % ~= 0.0 ns <= cpuacct_charge > 0.00 % ~= 0.0 ns <= clockevents_program_event > 0.00 % ~= 0.0 ns <= update_blocked_averages > Sum: 0.68 % => calc: 0.6 ns (sum: 0.6 ns) => Total: 82.7 ns > >
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