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Date: Tue, 9 Aug 2016 14:14:22 +0200
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>,
Rana Shahout <rana.shahot@...il.com>
Cc: Eric Dumazet <eric.dumazet@...il.com>,
Brenden Blanco <bblanco@...mgrid.com>, davem@...emloft.net,
netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
Saeed Mahameed <saeedm@....mellanox.co.il>,
Martin KaFai Lau <kafai@...com>, Ari Saha <as754m@....com>,
Or Gerlitz <gerlitz.or@...il.com>, john.fastabend@...il.com,
hannes@...essinduktion.org, Thomas Graf <tgraf@...g.ch>,
Tom Herbert <tom@...bertland.com>,
Daniel Borkmann <daniel@...earbox.net>,
Tariq Toukan <ttoukan.linux@...il.com>,
Mel Gorman <mgorman@...hsingularity.net>,
linux-mm <linux-mm@...ck.org>, brouer@...hat.com
Subject: Re: order-0 vs order-N driver allocation. Was: [PATCH v10 07/12]
net/mlx4_en: add page recycle to prepare rx ring for tx support
> > On Sun, 7 Aug 2016 19:15:27 -0700 Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
[...]
> > > could you please share the performance numbers for mlx5 order-0 vs order-N ?
> > > You mentioned that there was some performance improvement. We need to know
> > > how much we'll lose when we turn off order-N.
There is an really easy way (after XDP) to benchmark this
order-0 vs order-N, for the driver mlx4.
I simply load a XDP program, that returns XDP_PASS, because loading XDP
will reallocate the RX rings to use a single frame/packet and order-0
pages (for RX ring slots).
Result summary: (order-3 pages) 4,453,022 -> (XDP_PASS) 3,295,798 pps
* 3295798 - 4453022 = -1157224 pps slower
* (3295798/4453022-1)*100 = -25.98% slower
* (1/4453022-1/3295798)*10^9 - -78.85 nanosec slower
* Approx convert nanosec to cycles (78.85 * 4GHz) = 315 cycles slower
Where does this performance regression originate from. Well, this
basically only changed the page allocation strategy and number of DMA
calls in the driver. Thus, lets look at the performance of the page
allocator (see tool Page_bench_ and MM_slides_ page 9)
On this machine:
* Cost of order-0: 237 cycles(tsc) 59.336 ns
* Cost of order-3: 423 cycles(tsc) 106.029 ns
The order-3 cost is amortized, as it can store 21 frames of size 1536,
to cost per page-fragment 20 cycles / 5.049 ns. Thus, I would expect
to see a (59.336-5.049) 54.287 ns performance reduction, not 78.85,
which is 24.563 ns higher than expected (extra dma maps cannot explain
this on a Intel platform).
There is a higher percentage of L3/LLC-load-misses, which is strange,
as I though the simple XDP (inc map cnt and return XDP_PASS) program
should not touch the data. Quick experiment with xdp-prog that touch
data like xdp1 and always return XDP_PASS, show 3209235 with is only
8ns slower ((1/3209235-1/3295798)*10^9 = 8.184 ns). Thus, the extra
24ns (or 16ns) might originate from an earlier cache-miss.
Conclusion: These measurements confirm that we need a page recycle
facility for the drivers before switching to order-0 allocations.
Links:
.. _Page_bench: https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/bench/page_bench01.c
.. _MM_slides: http://people.netfilter.org/hawk/presentations/MM-summit2016/generic_page_pool_mm_summit2016.odp
Benchmarking notes and perf results below:
Base setup:
* Drop packets in iptables RAW
* Disable Ethernet flow control
* Disable GRO (changes driver code path)
* Mlx4 NIC CX3-pro (mlx4_core log_num_mgm_entry_size=-2)
* CPU: i7-4790K CPU @ 4.00GHz (turbostat report 4.3GHz)
Baseline: 4.7.0-baseline+ #102 SMP PREEMPT
* instant rx:4558943 tx:0 pps n:162 average: rx:4453022 tx:0 pps
(instant variation TX 0.000 ns (min:0.000 max:0.000) RX 5.217 ns)
Baseline perf stat::
$ sudo perf stat -C3 -e L1-icache-load-misses -e cycles:k -e instructions:k -e cache-misses:k -e cache-references:k -e LLC-store-misses:k -e LLC-store -e LLC-load-misses:k -e LLC-load -r 5 sleep 1
Performance counter stats for 'CPU(s) 3' (5 runs) ::
271,417 L1-icache-load-misses ( +- 0.69% ) (33.32%)
4,383,371,009 cycles:k ( +- 0.01% ) (44.51%)
7,587,502,193 instructions:k # 1.50 insns per cycle (+- 0.01% )(55.62%)
5,856,640 cache-misses:k # 48.435 % of all cache refs (+- 0.01% )(66.72%)
12,091,854 cache-references:k ( +- 0.04%)(66.72%)
451,681 LLC-store-misses ( +- 0.13%)(66.72%)
463,152 LLC-store ( +- 0.12%)(66.68%)
5,408,934 LLC-load-misses # 47.26% of all LL-cache hits (0.01%) (22.19%)
11,446,060 LLC-load ( +- 0.04%) (22.19%)
Samples: 40K of event 'cycles', Event count (approx.): 43956150960 ::
Overhead Command Shared Object Symbol
+ 36.59% ksoftirqd/3 [kernel.vmlinux] [k] memcpy_erms
+ 6.76% ksoftirqd/3 [mlx4_en] [k] mlx4_en_process_rx_cq
+ 6.66% ksoftirqd/3 [ip_tables] [k] ipt_do_table
+ 6.03% ksoftirqd/3 [kernel.vmlinux] [k] __build_skb
+ 4.65% ksoftirqd/3 [kernel.vmlinux] [k] ip_rcv
+ 4.22% ksoftirqd/3 [mlx4_en] [k] mlx4_en_prepare_rx_desc
+ 3.46% ksoftirqd/3 [mlx4_en] [k] mlx4_en_free_frag
+ 3.37% ksoftirqd/3 [kernel.vmlinux] [k] __netif_receive_skb_core
+ 3.04% ksoftirqd/3 [kernel.vmlinux] [k] __netdev_alloc_skb
+ 2.80% ksoftirqd/3 [kernel.vmlinux] [k] kmem_cache_alloc
+ 2.38% ksoftirqd/3 [kernel.vmlinux] [k] __free_page_frag
+ 1.88% ksoftirqd/3 [kernel.vmlinux] [k] kmem_cache_free
+ 1.65% ksoftirqd/3 [kernel.vmlinux] [k] nf_iterate
+ 1.59% ksoftirqd/3 [kernel.vmlinux] [k] nf_hook_slow
+ 1.31% ksoftirqd/3 [kernel.vmlinux] [k] __rcu_read_unlock
+ 0.91% ksoftirqd/3 [kernel.vmlinux] [k] __alloc_page_frag
+ 0.88% ksoftirqd/3 [kernel.vmlinux] [k] eth_type_trans
+ 0.77% ksoftirqd/3 [kernel.vmlinux] [k] dev_gro_receive
+ 0.76% ksoftirqd/3 [kernel.vmlinux] [k] skb_release_data
+ 0.76% ksoftirqd/3 [kernel.vmlinux] [k] __local_bh_enable_ip
+ 0.72% ksoftirqd/3 [kernel.vmlinux] [k] netif_receive_skb_internal
+ 0.66% ksoftirqd/3 [kernel.vmlinux] [k] napi_gro_receive
+ 0.66% ksoftirqd/3 [kernel.vmlinux] [k] __rcu_read_lock
+ 0.65% ksoftirqd/3 [kernel.vmlinux] [k] skb_release_head_state
+ 0.57% ksoftirqd/3 [kernel.vmlinux] [k] get_page_from_freelist
+ 0.57% ksoftirqd/3 [kernel.vmlinux] [k] __free_pages_ok
+ 0.51% ksoftirqd/3 [kernel.vmlinux] [k] kfree_skb
+ 0.43% ksoftirqd/3 [kernel.vmlinux] [k] skb_release_all
Result-xdp-pass: loading XDP_PASS program
* instant rx:3374269 tx:0 pps n:537 average: rx:3295798 tx:0 pps
(instant variation TX 0.000 ns (min:0.000 max:0.000) RX 7.056 ns)
Difference: 4,453,022 -> 3,295,798 pps
* 3295798 - 4453022 = -1157224 pps slower
* (3295798/4453022-1)*100 = -25.98% slower
* (1/4453022-1/3295798)*10^9 - -78.85 nanosec slower
Perf stats xdp-pass::
Performance counter stats for 'CPU(s) 3' (5 runs):
294,219 L1-icache-load-misses (+-0.25% ) (33.33%)
4,382,764,897 cycles:k (+-0.00% ) (44.51%)
7,223,252,624 instructions:k # 1.65 insns per cycle (+-0.00%)(55.62%)
7,166,907 cache-misses:k # 58.792 % of all cache refs (+-0.01%)(66.72%)
12,190,275 cache-references:k (+-0.03% ) (66.72%)
525,262 LLC-store-misses (+-0.11% ) (66.72%)
587,354 LLC-store (+-0.09% ) (66.68%)
6,647,957 LLC-load-misses # 58.23% of all LL-cache hits (+-0.02%)(22.19%)
11,417,001 LLC-load (+-0.03%)(22.19%)
There is a higher percentage of L3/LLC-load-misses, which is strange,
as I though the simple XDP (return XDP_PASS and inc map cnt) program
would not touch the data.
Perf report xdp-pass::
Samples: 40K of event 'cycles', Event count (approx.): 43953682891
Overhead Command Shared Object Symbol
+ 25.79% ksoftirqd/3 [kernel.vmlinux] [k] memcpy_erms
+ 7.29% ksoftirqd/3 [mlx4_en] [k] mlx4_en_process_rx_cq
+ 5.42% ksoftirqd/3 [mlx4_en] [k] mlx4_en_free_frag
+ 5.16% ksoftirqd/3 [kernel.vmlinux] [k] get_page_from_freelist
+ 4.55% ksoftirqd/3 [ip_tables] [k] ipt_do_table
+ 4.46% ksoftirqd/3 [mlx4_en] [k] mlx4_alloc_pages.isra.19
+ 3.97% ksoftirqd/3 [kernel.vmlinux] [k] __build_skb
+ 3.67% ksoftirqd/3 [kernel.vmlinux] [k] free_hot_cold_page
+ 3.46% ksoftirqd/3 [kernel.vmlinux] [k] ip_rcv
+ 2.71% ksoftirqd/3 [kernel.vmlinux] [k] __alloc_pages_nodemask
+ 2.62% ksoftirqd/3 [kernel.vmlinux] [k] __netif_receive_skb_core
+ 2.46% ksoftirqd/3 [kernel.vmlinux] [k] kmem_cache_alloc
+ 2.24% ksoftirqd/3 [kernel.vmlinux] [k] __netdev_alloc_skb
+ 2.15% ksoftirqd/3 [mlx4_en] [k] mlx4_en_prepare_rx_desc
+ 1.88% ksoftirqd/3 [kernel.vmlinux] [k] __free_page_frag
+ 1.55% ksoftirqd/3 [kernel.vmlinux] [k] kmem_cache_free
+ 1.42% ksoftirqd/3 [kernel.vmlinux] [k] __rcu_read_unlock
+ 1.27% ksoftirqd/3 [kernel.vmlinux] [k] nf_iterate
+ 1.14% ksoftirqd/3 [kernel.vmlinux] [k] nf_hook_slow
+ 1.05% ksoftirqd/3 [kernel.vmlinux] [k] alloc_pages_current
+ 0.83% ksoftirqd/3 [kernel.vmlinux] [k] __inc_zone_state
+ 0.73% ksoftirqd/3 [kernel.vmlinux] [k] __list_del_entry
+ 0.69% ksoftirqd/3 [kernel.vmlinux] [k] __list_add
+ 0.64% ksoftirqd/3 [kernel.vmlinux] [k] __local_bh_enable_ip
+ 0.64% ksoftirqd/3 [kernel.vmlinux] [k] __rcu_read_lock
+ 0.62% ksoftirqd/3 [kernel.vmlinux] [k] dev_gro_receive
+ 0.62% ksoftirqd/3 [kernel.vmlinux] [k] swiotlb_map_page
+ 0.61% ksoftirqd/3 [kernel.vmlinux] [k] skb_release_data
+ 0.60% ksoftirqd/3 [kernel.vmlinux] [k] __alloc_page_frag
+ 0.58% ksoftirqd/3 [kernel.vmlinux] [k] eth_type_trans
+ 0.57% ksoftirqd/3 [kernel.vmlinux] [k] policy_zonelist
+ 0.51% ksoftirqd/3 [pps_core] [k] 0x000000000000692d
+ 0.51% ksoftirqd/3 [kernel.vmlinux] [k] netif_receive_skb_internal
+ 0.50% ksoftirqd/3 [kernel.vmlinux] [k] napi_gro_receive
+ 0.49% ksoftirqd/3 [kernel.vmlinux] [k] __put_page
+ 0.49% ksoftirqd/3 [kernel.vmlinux] [k] skb_release_head_state
+ 0.42% ksoftirqd/3 [kernel.vmlinux] [k] kfree_skb
+ 0.34% ksoftirqd/3 [pps_core] [k] 0x0000000000006935
+ 0.33% ksoftirqd/3 [kernel.vmlinux] [k] skb_free_head
+ 0.32% ksoftirqd/3 [kernel.vmlinux] [k] __netif_receive_skb
+ 0.31% ksoftirqd/3 [kernel.vmlinux] [k] swiotlb_sync_single
+ 0.31% ksoftirqd/3 [kernel.vmlinux] [k] skb_gro_reset_offset
+ 0.29% ksoftirqd/3 [kernel.vmlinux] [k] swiotlb_sync_single_for_cpu
+ 0.29% ksoftirqd/3 [kernel.vmlinux] [k] list_del
+ 0.27% ksoftirqd/3 [iptable_raw] [k] iptable_raw_hook
+ 0.27% ksoftirqd/3 [kernel.vmlinux] [k] skb_release_all
+ 0.26% ksoftirqd/3 [kernel.vmlinux] [k] kfree_skbmem
+ 0.25% ksoftirqd/3 [kernel.vmlinux] [k] swiotlb_unmap_page
+ 0.23% ksoftirqd/3 [kernel.vmlinux] [k] bpf_map_lookup_elem
+ 0.22% ksoftirqd/3 [kernel.vmlinux] [k] percpu_array_map_lookup_elem
+ 0.20% ksoftirqd/3 [kernel.vmlinux] [k] __page_cache_release
In perf-diff notice the increase for:
* get_page_from_freelist(0.57%) +4.59%,
* mlx4_en_free_frag (3.46%) +1.96%,
* mlx4_alloc_pages (0.26%) +4.20%
* __alloc_pages_nodemask(0.14%) +2.57%
* swiotlb_map_page (0.04%) +0.57%
Perf diff::
# Baseline Delta Shared Object Symbol
# ........ ....... ................... ................................
#
36.59% -10.80% [kernel.vmlinux] [k] memcpy_erms
6.76% +0.53% [mlx4_en] [k] mlx4_en_process_rx_cq
6.66% -2.11% [ip_tables] [k] ipt_do_table
6.03% -2.06% [kernel.vmlinux] [k] __build_skb
4.65% -1.18% [kernel.vmlinux] [k] ip_rcv
4.22% -2.06% [mlx4_en] [k] mlx4_en_prepare_rx_desc
3.46% +1.96% [mlx4_en] [k] mlx4_en_free_frag
3.37% -0.75% [kernel.vmlinux] [k] __netif_receive_skb_core
3.04% -0.80% [kernel.vmlinux] [k] __netdev_alloc_skb
2.80% -0.34% [kernel.vmlinux] [k] kmem_cache_alloc
2.38% -0.50% [kernel.vmlinux] [k] __free_page_frag
1.88% -0.34% [kernel.vmlinux] [k] kmem_cache_free
1.65% -0.38% [kernel.vmlinux] [k] nf_iterate
1.59% -0.45% [kernel.vmlinux] [k] nf_hook_slow
1.31% +0.11% [kernel.vmlinux] [k] __rcu_read_unlock
0.91% -0.31% [kernel.vmlinux] [k] __alloc_page_frag
0.88% -0.30% [kernel.vmlinux] [k] eth_type_trans
0.77% -0.15% [kernel.vmlinux] [k] dev_gro_receive
0.76% -0.15% [kernel.vmlinux] [k] skb_release_data
0.76% -0.12% [kernel.vmlinux] [k] __local_bh_enable_ip
0.72% -0.21% [kernel.vmlinux] [k] netif_receive_skb_internal
0.66% -0.16% [kernel.vmlinux] [k] napi_gro_receive
0.66% -0.02% [kernel.vmlinux] [k] __rcu_read_lock
0.65% -0.17% [kernel.vmlinux] [k] skb_release_head_state
0.57% +4.59% [kernel.vmlinux] [k] get_page_from_freelist
0.57% [kernel.vmlinux] [k] __free_pages_ok
0.51% -0.09% [kernel.vmlinux] [k] kfree_skb
0.43% -0.15% [kernel.vmlinux] [k] skb_release_all
0.42% -0.11% [kernel.vmlinux] [k] skb_gro_reset_offset
0.41% -0.08% [kernel.vmlinux] [k] skb_free_head
0.39% -0.07% [kernel.vmlinux] [k] __netif_receive_skb
0.36% -0.08% [iptable_raw] [k] iptable_raw_hook
0.34% -0.08% [kernel.vmlinux] [k] kfree_skbmem
0.28% +0.01% [kernel.vmlinux] [k] swiotlb_sync_single_for_cpu
0.26% +4.20% [mlx4_en] [k] mlx4_alloc_pages.isra.19
0.20% +0.11% [kernel.vmlinux] [k] swiotlb_sync_single
0.15% -0.03% [kernel.vmlinux] [k] __do_softirq
0.14% +2.57% [kernel.vmlinux] [k] __alloc_pages_nodemask
0.14% [kernel.vmlinux] [k] free_one_page
0.13% -0.13% [kernel.vmlinux] [k] _raw_spin_lock_irqsave
0.13% -0.12% [kernel.vmlinux] [k] _raw_spin_lock
0.10% [kernel.vmlinux] [k] __mod_zone_page_state
0.09% +0.06% [kernel.vmlinux] [k] net_rx_action
0.09% [kernel.vmlinux] [k] __rmqueue
0.07% [kernel.vmlinux] [k] __zone_watermark_ok
0.07% [kernel.vmlinux] [k] PageHuge
0.06% +0.77% [kernel.vmlinux] [k] __inc_zone_state
0.76% -0.15% [kernel.vmlinux] [k] skb_release_data
0.76% -0.12% [kernel.vmlinux] [k] __local_bh_enable_ip
0.72% -0.21% [kernel.vmlinux] [k] netif_receive_skb_internal
0.66% -0.16% [kernel.vmlinux] [k] napi_gro_receive
0.66% -0.02% [kernel.vmlinux] [k] __rcu_read_lock
0.65% -0.17% [kernel.vmlinux] [k] skb_release_head_state
0.57% +4.59% [kernel.vmlinux] [k] get_page_from_freelist
0.57% [kernel.vmlinux] [k] __free_pages_ok
0.51% -0.09% [kernel.vmlinux] [k] kfree_skb
0.43% -0.15% [kernel.vmlinux] [k] skb_release_all
0.42% -0.11% [kernel.vmlinux] [k] skb_gro_reset_offset
0.41% -0.08% [kernel.vmlinux] [k] skb_free_head
0.39% -0.07% [kernel.vmlinux] [k] __netif_receive_skb
0.36% -0.08% [iptable_raw] [k] iptable_raw_hook
0.34% -0.08% [kernel.vmlinux] [k] kfree_skbmem
0.28% +0.01% [kernel.vmlinux] [k] swiotlb_sync_single_for_cpu
0.26% +4.20% [mlx4_en] [k] mlx4_alloc_pages.isra.19
0.20% +0.11% [kernel.vmlinux] [k] swiotlb_sync_single
0.15% -0.03% [kernel.vmlinux] [k] __do_softirq
0.14% +2.57% [kernel.vmlinux] [k] __alloc_pages_nodemask
0.14% [kernel.vmlinux] [k] free_one_page
0.13% -0.13% [kernel.vmlinux] [k] _raw_spin_lock_irqsave
0.13% -0.12% [kernel.vmlinux] [k] _raw_spin_lock
0.10% [kernel.vmlinux] [k] __mod_zone_page_state
0.09% +0.06% [kernel.vmlinux] [k] net_rx_action
0.09% [kernel.vmlinux] [k] __rmqueue
0.07% [kernel.vmlinux] [k] __zone_watermark_ok
0.07% [kernel.vmlinux] [k] PageHuge
0.06% +0.77% [kernel.vmlinux] [k] __inc_zone_state
0.06% +0.98% [kernel.vmlinux] [k] alloc_pages_current
0.06% +0.51% [kernel.vmlinux] [k] policy_zonelist
0.06% +0.01% [kernel.vmlinux] [k] delay_tsc
0.05% -0.00% [mlx4_en] [k] mlx4_en_poll_rx_cq
0.05% +0.01% [kernel.vmlinux] [k] __memcpy
0.04% +0.57% [kernel.vmlinux] [k] swiotlb_map_page
0.04% +0.69% [kernel.vmlinux] [k] __list_del_entry
0.04% [kernel.vmlinux] [k] free_compound_page
0.04% [kernel.vmlinux] [k] __put_compound_page
0.03% +0.66% [kernel.vmlinux] [k] __list_add
--
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
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