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Commit c4b2bf6b authored by Tonghao Zhang's avatar Tonghao Zhang Committed by David S. Miller
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openvswitch: Optimize operations for OvS flow_stats. 



When calling the flow_free() to free the flow, we call many times
(cpu_possible_mask, eg. 128 as default) cpumask_next(). That will
take up our CPU usage if we call the flow_free() frequently.
When we put all packets to userspace via upcall, and OvS will send
them back via netlink to ovs_packet_cmd_execute(will call flow_free).

The test topo is shown as below. VM01 sends TCP packets to VM02,
and OvS forward packtets. When testing, we use perf to report the
system performance.

VM01 --- OvS-VM --- VM02

Without this patch, perf-top show as below: The flow_free() is
3.02% CPU usage.

	4.23%  [kernel]            [k] _raw_spin_unlock_irqrestore
	3.62%  [kernel]            [k] __do_softirq
	3.16%  [kernel]            [k] __memcpy
	3.02%  [kernel]            [k] flow_free
	2.42%  libc-2.17.so        [.] __memcpy_ssse3_back
	2.18%  [kernel]            [k] copy_user_generic_unrolled
	2.17%  [kernel]            [k] find_next_bit

When applied this patch, perf-top show as below: Not shown on
the list anymore.

	4.11%  [kernel]            [k] _raw_spin_unlock_irqrestore
	3.79%  [kernel]            [k] __do_softirq
	3.46%  [kernel]            [k] __memcpy
	2.73%  libc-2.17.so        [.] __memcpy_ssse3_back
	2.25%  [kernel]            [k] copy_user_generic_unrolled
	1.89%  libc-2.17.so        [.] _int_malloc
	1.53%  ovs-vswitchd        [.] xlate_actions

With this patch, the TCP throughput(we dont use Megaflow Cache
+ Microflow Cache) between VMs is 1.18Gbs/sec up to 1.30Gbs/sec
(maybe ~10% performance imporve).

This patch adds cpumask struct, the cpu_used_mask stores the cpu_id
that the flow used. And we only check the flow_stats on the cpu we
used, and it is unncessary to check all possible cpu when getting,
cleaning, and updating the flow_stats. Adding the cpu_used_mask to
sw_flow struct does’t increase the cacheline number.

Signed-off-by: default avatarTonghao Zhang <xiangxia.m.yue@gmail.com>
Acked-by: default avatarPravin B Shelar <pshelar@ovn.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c57c054e

net/openvswitch/flow.c

+4 −3
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ void ovs_flow_stats_update(struct sw_flow *flow, __be16 tcp_flags, 
			   const struct sk_buff *skb)

{

	struct flow_stats *stats;

	int cpu = smp_processor_id();

	unsigned int cpu = smp_processor_id();

	int len = skb->len + (skb_vlan_tag_present(skb) ? VLAN_HLEN : 0);



	stats = rcu_dereference(flow->stats[cpu]);
@@ -117,6 +117,7 @@ void ovs_flow_stats_update(struct sw_flow *flow, __be16 tcp_flags, 


					rcu_assign_pointer(flow->stats[cpu],

							   new_stats);

					cpumask_set_cpu(cpu, &flow->cpu_used_mask);

					goto unlock;

				}

			}
@@ -144,7 +145,7 @@ void ovs_flow_stats_get(const struct sw_flow *flow, 
	memset(ovs_stats, 0, sizeof(*ovs_stats));



	/* We open code this to make sure cpu 0 is always considered */

	for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, cpu_possible_mask)) {

	for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, &flow->cpu_used_mask)) {

		struct flow_stats *stats = rcu_dereference_ovsl(flow->stats[cpu]);



		if (stats) {
@@ -168,7 +169,7 @@ void ovs_flow_stats_clear(struct sw_flow *flow) 
	int cpu;



	/* We open code this to make sure cpu 0 is always considered */

	for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, cpu_possible_mask)) {

	for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, &flow->cpu_used_mask)) {

		struct flow_stats *stats = ovsl_dereference(flow->stats[cpu]);



		if (stats) {

net/openvswitch/flow.h

+2 −0
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ 
#include <linux/jiffies.h>

#include <linux/time.h>

#include <linux/flex_array.h>

#include <linux/cpumask.h>

#include <net/inet_ecn.h>

#include <net/ip_tunnels.h>

#include <net/dst_metadata.h>
@@ -219,6 +220,7 @@ struct sw_flow { 
					 */

	struct sw_flow_key key;

	struct sw_flow_id id;

	struct cpumask cpu_used_mask;

	struct sw_flow_mask *mask;

	struct sw_flow_actions __rcu *sf_acts;

	struct flow_stats __rcu *stats[]; /* One for each CPU.  First one

net/openvswitch/flow_table.c

+3 −1
Original line number Diff line number Diff line
@@ -98,6 +98,8 @@ struct sw_flow *ovs_flow_alloc(void) 


	RCU_INIT_POINTER(flow->stats[0], stats);



	cpumask_set_cpu(0, &flow->cpu_used_mask);



	return flow;

err:

	kmem_cache_free(flow_cache, flow);
@@ -141,7 +143,7 @@ static void flow_free(struct sw_flow *flow) 
	if (flow->sf_acts)

		ovs_nla_free_flow_actions((struct sw_flow_actions __force *)flow->sf_acts);

	/* We open code this to make sure cpu 0 is always considered */

	for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, cpu_possible_mask))

	for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, &flow->cpu_used_mask))

		if (flow->stats[cpu])

			kmem_cache_free(flow_stats_cache,

					(struct flow_stats __force *)flow->stats[cpu]);