Re: [ovs-dev] [PATCH net-next v3 1/1] net:openvswitch:reduce cpu_used_mask memory

[Eelco Chaudron]

On 2 Feb 2023, at 13:40, 陶 缘 wrote:

> Hi, Eelco:
>
>        I have a query regarding to the style check.
> Though the './scripts/checkpatch.pl' emit no warning/error, the 'netdev/checkpatch' still has one warning "WARNING: line length of 82 exceeds 80 columns"
> I went through the patch line by line and could not find any changed line exceeding the 80 character limit.
>
> I am afraid that the netdev/checkpatch takes counts on the removed line(old removed line has length exceeding 80 and i have revised that in the patch already
>
> Is there any known issue regarding to the netdev/checkpatch?

Not sure which netdev/checkpatch you are referring to. I always you the general kernel one in /script/checkpatch.pl.


Your patch looks good to me with /script/checkpatch.pl --strict.

> Best regards
>
> eddy
>
> ________________________________
> 发件人: Eelco Chaudron <echaudro@xxxxxxxxxx>
> 发送时间: 2023年2月2日 11:44
> 收件人: 陶 缘 <taoyuan_eddy@xxxxxxxxxxx>
> 抄送: netdev@xxxxxxxxxxxxxxx <netdev@xxxxxxxxxxxxxxx>; dev@xxxxxxxxxxxxxxx <dev@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx <linux-kernel@xxxxxxxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>
> 主题: Re: [ovs-dev] [PATCH net-next v3 1/1] net:openvswitch:reduce cpu_used_mask memory
>
>
>
> On 2 Feb 2023, at 12:26, 陶 缘 wrote:
>
>> Hi, Eelco:
>>
>>       Thanks for your time going through the detail.
>> The thing is: sizeof(struct cpumask), with default CONFIG_NR_CPUS 8192, has a size of 1024 bytes even on a system with only 4 cpus.
>> While in practice the cpumask APIs like cpumask_next and cpumask_set_cpu never access more than cpumask_size() of bytes in the bitmap
>> My change used cpumask_size() (in above example, consume 8 bytes after alignement for the cpumask, it saved 1016 bytes for every flow.
>
> I looked at the wrong nr_cpumask_bits definition, so thanks for this education :)
>
>> Your question reminded me to revisit the description "as well as the iteration of bits in cpu_used_mask", after a second think, this statement is not valid and should be removed.
>> since the iteration API will not access the number of bytes decided by nr_cpu_ids(running CPUs)
>>
>> I will remove this statement after solving a final style issue in the next submission.
>
> Thanks!
>
>
>> Thanks
>> eddy
>> ________________________________
>> 发件人: Eelco Chaudron <echaudro@xxxxxxxxxx>
>> 发送时间: 2023年2月2日 11:05
>> 收件人: Eddy Tao <taoyuan_eddy@xxxxxxxxxxx>
>> 抄送: netdev@xxxxxxxxxxxxxxx <netdev@xxxxxxxxxxxxxxx>; dev@xxxxxxxxxxxxxxx <dev@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx <linux-kernel@xxxxxxxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>
>> 主题: Re: [ovs-dev] [PATCH net-next v3 1/1] net:openvswitch:reduce cpu_used_mask memory
>>
>>
>>
>> On 2 Feb 2023, at 11:32, Eddy Tao wrote:
>>
>>> Use actual CPU number instead of hardcoded value to decide the size
>>> of 'cpu_used_mask' in 'struct sw_flow'. Below is the reason.
>>>
>>> 'struct cpumask cpu_used_mask' is embedded in struct sw_flow.
>>> Its size is hardcoded to CONFIG_NR_CPUS bits, which can be
>>> 8192 by default, it costs memory and slows down ovs_flow_alloc
>>> as well as the iteration of bits in cpu_used_mask when handling
>>> netlink message from ofproto
>>
>> I’m trying to understand how this will decrease memory usage. The size of the flow_cache stayed the same (actually it’s large due to the extra pointer).
>>
>> Also do not understand why the iteration is less, as the mask is initialized the same.
>>
>> Cheers,
>>
>> Eelco
>>
>>> To address this, redefine cpu_used_mask to pointer
>>> append cpumask_size() bytes after 'stat' to hold cpumask
>>>
>>> cpumask APIs like cpumask_next and cpumask_set_cpu never access
>>> bits beyond cpu count, cpumask_size() bytes of memory is enough
>>>
>>> Signed-off-by: Eddy Tao <taoyuan_eddy@xxxxxxxxxxx>
>>> ---
>>>  net/openvswitch/flow.c       | 8 +++++---
>>>  net/openvswitch/flow.h       | 2 +-
>>>  net/openvswitch/flow_table.c | 8 +++++---
>>>  3 files changed, 11 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
>>> index e20d1a973417..0109a5f86f6a 100644
>>> --- a/net/openvswitch/flow.c
>>> +++ b/net/openvswitch/flow.c
>>> @@ -107,7 +107,7 @@ 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);
>>> +                                     cpumask_set_cpu(cpu, flow->cpu_used_mask);
>>>                                        goto unlock;
>>>                                }
>>>                        }
>>> @@ -135,7 +135,8 @@ 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, &flow->cpu_used_mask)) {
>>> +     for (cpu = 0; cpu < nr_cpu_ids;
>>> +          cpu = cpumask_next(cpu, flow->cpu_used_mask)) {
>>>                struct sw_flow_stats *stats = rcu_dereference_ovsl(flow->stats[cpu]);
>>>
>>>                if (stats) {
>>> @@ -159,7 +160,8 @@ 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, &flow->cpu_used_mask)) {
>>> +     for (cpu = 0; cpu < nr_cpu_ids;
>>> +          cpu = cpumask_next(cpu, flow->cpu_used_mask)) {
>>>                struct sw_flow_stats *stats = ovsl_dereference(flow->stats[cpu]);
>>>
>>>                if (stats) {
>>> diff --git a/net/openvswitch/flow.h b/net/openvswitch/flow.h
>>> index 073ab73ffeaa..b5711aff6e76 100644
>>> --- a/net/openvswitch/flow.h
>>> +++ b/net/openvswitch/flow.h
>>> @@ -229,7 +229,7 @@ struct sw_flow {
>>>                                         */
>>>        struct sw_flow_key key;
>>>        struct sw_flow_id id;
>>> -     struct cpumask cpu_used_mask;
>>> +     struct cpumask *cpu_used_mask;
>>>        struct sw_flow_mask *mask;
>>>        struct sw_flow_actions __rcu *sf_acts;
>>>        struct sw_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 0a0e4c283f02..dc6a174c3194 100644
>>> --- a/net/openvswitch/flow_table.c
>>> +++ b/net/openvswitch/flow_table.c
>>> @@ -87,11 +87,12 @@ struct sw_flow *ovs_flow_alloc(void)
>>>        if (!stats)
>>>                goto err;
>>>
>>> +     flow->cpu_used_mask = (struct cpumask *)&flow->stats[nr_cpu_ids];
>>>        spin_lock_init(&stats->lock);
>>>
>>>        RCU_INIT_POINTER(flow->stats[0], stats);
>>>
>>> -     cpumask_set_cpu(0, &flow->cpu_used_mask);
>>> +     cpumask_set_cpu(0, flow->cpu_used_mask);
>>>
>>>        return flow;
>>>  err:
>>> @@ -115,7 +116,7 @@ static void flow_free(struct sw_flow *flow)
>>>                                          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, &flow->cpu_used_mask)) {
>>> +          cpu = cpumask_next(cpu, flow->cpu_used_mask)) {
>>>                if (flow->stats[cpu])
>>>                        kmem_cache_free(flow_stats_cache,
>>>                                        (struct sw_flow_stats __force *)flow->stats[cpu]);
>>> @@ -1196,7 +1197,8 @@ int ovs_flow_init(void)
>>>
>>>        flow_cache = kmem_cache_create("sw_flow", sizeof(struct sw_flow)
>>>                                       + (nr_cpu_ids
>>> -                                       * sizeof(struct sw_flow_stats *)),
>>> +                                       * sizeof(struct sw_flow_stats *))
>>> +                                    + cpumask_size(),
>>>                                       0, 0, NULL);
>>>        if (flow_cache == NULL)
>>>                return -ENOMEM;
>>> --
>>> 2.27.0
>>>
>>> _______________________________________________
>>> dev mailing list
>>> dev@xxxxxxxxxxxxxxx
>>> https://mail.openvswitch.org/mailman/listinfo/ovs-dev