Re: [PATCH][net-next] openvswitch: eliminate cpu_used_mask from sw_flow

2018-07-29 Thread David Miller
From: Li RongQing 
Date: Fri, 27 Jul 2018 16:03:57 +0800

> The size of struct cpumask varies with CONFIG_NR_CPUS, some config
> CONFIG_NR_CPUS is very larger, like 5120, struct cpumask will take
> 640 bytes, if there is thousands of flows, it will take lots of
> memory
> 
> cpu_used_mask has two purposes
> 1: Assume first cpu as cpu0 which maybe not true; now use
>cpumask_first(cpu_possible_mask)
> 2: when get/clear statistic, reduce the iteratation; but it
>is not hot path, so use for_each_possible_cpu
> 
> Signed-off-by: Zhang Yu 
> Signed-off-by: Li RongQing 

This seems to completely undo the optimization done by:

commit c4b2bf6b4a35348fe6d1eb06928eb68d7b9d99a9
Author: Tonghao Zhang 
Date:   Mon Jul 17 23:28:06 2017 -0700

openvswitch: Optimize operations for OvS flow_stats.

And in that commit message it states clearly that flow_free()
performance matters, and that the iteration over cpu_possible_mask in
the for() loop is the problem.

At a minimum, we can't apply this unless you explain why the
above performance issue won't be reintroudced by your change.

Thank you.


Re: [PATCH][net-next] openvswitch: eliminate cpu_used_mask from sw_flow

2018-07-28 Thread Pravin Shelar
On Fri, Jul 27, 2018 at 1:03 AM, Li RongQing  wrote:
> The size of struct cpumask varies with CONFIG_NR_CPUS, some config
> CONFIG_NR_CPUS is very larger, like 5120, struct cpumask will take
> 640 bytes, if there is thousands of flows, it will take lots of
> memory
>
I am fine with removing cpumask bitmap from flow struct.

> cpu_used_mask has two purposes
> 1: Assume first cpu as cpu0 which maybe not true; now use
>cpumask_first(cpu_possible_mask)

I am not sure about this, most of system would have cpu zero, so why
this change is done in this patch ? This adds overhead of calculating
first cpu when updating stats in fast path.

> 2: when get/clear statistic, reduce the iteratation; but it
>is not hot path, so use for_each_possible_cpu
>


[PATCH][net-next] openvswitch: eliminate cpu_used_mask from sw_flow

2018-07-27 Thread Li RongQing
The size of struct cpumask varies with CONFIG_NR_CPUS, some config
CONFIG_NR_CPUS is very larger, like 5120, struct cpumask will take
640 bytes, if there is thousands of flows, it will take lots of
memory

cpu_used_mask has two purposes
1: Assume first cpu as cpu0 which maybe not true; now use
   cpumask_first(cpu_possible_mask)
2: when get/clear statistic, reduce the iteratation; but it
   is not hot path, so use for_each_possible_cpu

Signed-off-by: Zhang Yu 
Signed-off-by: Li RongQing 
---
 net/openvswitch/flow.c   | 11 +--
 net/openvswitch/flow.h   |  5 ++---
 net/openvswitch/flow_table.c | 11 +--
 3 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index 56b8e7167790..ad580bec00fb 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -85,7 +85,9 @@ void ovs_flow_stats_update(struct sw_flow *flow, __be16 
tcp_flags,
if (cpu == 0 && unlikely(flow->stats_last_writer != cpu))
flow->stats_last_writer = cpu;
} else {
-   stats = rcu_dereference(flow->stats[0]); /* Pre-allocated. */
+   int cpu1 = cpumask_first(cpu_possible_mask);
+
+   stats = rcu_dereference(flow->stats[cpu1]); /* Pre-allocated. */
spin_lock(>lock);
 
/* If the current CPU is the only writer on the
@@ -118,7 +120,6 @@ void ovs_flow_stats_update(struct sw_flow *flow, __be16 
tcp_flags,
 
rcu_assign_pointer(flow->stats[cpu],
   new_stats);
-   cpumask_set_cpu(cpu, 
>cpu_used_mask);
goto unlock;
}
}
@@ -145,8 +146,7 @@ void ovs_flow_stats_get(const struct sw_flow *flow,
*tcp_flags = 0;
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_used_mask)) {
+   for_each_possible_cpu(cpu) {
struct flow_stats *stats = 
rcu_dereference_ovsl(flow->stats[cpu]);
 
if (stats) {
@@ -169,8 +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_used_mask)) {
+   for_each_possible_cpu(cpu) {
struct flow_stats *stats = ovsl_dereference(flow->stats[cpu]);
 
if (stats) {
diff --git a/net/openvswitch/flow.h b/net/openvswitch/flow.h
index c670dd24b8b7..d0ea5d6ced3e 100644
--- a/net/openvswitch/flow.h
+++ b/net/openvswitch/flow.h
@@ -223,17 +223,16 @@ struct sw_flow {
u32 hash;
} flow_table, ufid_table;
int stats_last_writer;  /* CPU id of the last writer on
-* 'stats[0]'.
+* 'stats[first cpu id]'.
 */
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
   * is allocated at flow creation time,
   * the rest are allocated on demand
-  * while holding the 'stats[0].lock'.
+  * while holding the 'stats[first cpu 
id].lock'
   */
 };
 
diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
index 80ea2a71852e..e4dbd65c308a 100644
--- a/net/openvswitch/flow_table.c
+++ b/net/openvswitch/flow_table.c
@@ -80,6 +80,7 @@ struct sw_flow *ovs_flow_alloc(void)
 {
struct sw_flow *flow;
struct flow_stats *stats;
+   int cpu = cpumask_first(cpu_possible_mask);
 
flow = kmem_cache_zalloc(flow_cache, GFP_KERNEL);
if (!flow)
@@ -90,15 +91,13 @@ struct sw_flow *ovs_flow_alloc(void)
/* Initialize the default stat node. */
stats = kmem_cache_alloc_node(flow_stats_cache,
  GFP_KERNEL | __GFP_ZERO,
- node_online(0) ? 0 : NUMA_NO_NODE);
+ cpu_to_node(cpu));
if (!stats)
goto err;
 
spin_lock_init(>lock);
 
-   RCU_INIT_POINTER(flow->stats[0], stats);
-
-   cpumask_set_cpu(0, >cpu_used_mask);
+   RCU_INIT_POINTER(flow->stats[cpu], stats);
 
return flow;
 err:
@@ -142,11 +141,11 @@ static void flow_free(struct sw_flow *flow)
kfree(flow->id.unmasked_key);
if (flow->sf_acts)