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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: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tonghao Zhang 2017-07-17 23:28:06 -07:00 committed by David S. Miller
parent c57c054eb5
commit c4b2bf6b4a
3 changed files with 9 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
net/openvswitch/flow.c
View File

@ -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) {

2
net/openvswitch/flow.h
View File

@ -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

4
net/openvswitch/flow_table.c
View File

@ -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]);