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....@gmail.com>
---
 net/openvswitch/flow.c       | 7 ++++---
 net/openvswitch/flow.h       | 2 ++
 net/openvswitch/flow_table.c | 5 ++++-
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index 89aeb32..cfb652a 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -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) {
diff --git a/net/openvswitch/flow.h b/net/openvswitch/flow.h
index a9bc1c8..1875bba 100644
--- a/net/openvswitch/flow.h
+++ b/net/openvswitch/flow.h
@@ -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
diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
index ea7a807..324a246 100644
--- a/net/openvswitch/flow_table.c
+++ b/net/openvswitch/flow_table.c
@@ -98,6 +98,9 @@ struct sw_flow *ovs_flow_alloc(void)
 
        RCU_INIT_POINTER(flow->stats[0], stats);
 
+       cpumask_clear(&flow->cpu_used_mask);
+       cpumask_set_cpu(0, &flow->cpu_used_mask);
+
        return flow;
 err:
        kmem_cache_free(flow_cache, flow);
@@ -141,7 +144,7 @@ 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]);
-- 
1.8.3.1

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