Re: [PATCH net-next v2 2/2] net: sched: Lockless Token Bucket (LTB) qdisc

[Eric Dumazet]

On 7/8/20 5:58 PM, YU, Xiangning wrote:
> 
> 
> On 7/8/20 5:08 PM, Eric Dumazet wrote:
>>
>>
>> On 7/8/20 4:59 PM, YU, Xiangning wrote:
>>
>>>
>>> Yes, we are touching a cache line here to make sure aggregation tasklet is 
>>> scheduled immediately. In most cases it is a call to test_and_set_bit(). 
>>
>>
>> test_and_set_bit() is dirtying the cache line even if the bit is already set.
>>
> 
> Yes. I do hope we can avoid this.
> 
>>>
>>> We might be able to do some inline processing without tasklet here, still 
>>> we need to make sure the aggregation won't run simultaneously on multiple 
>>> CPUs. 
>>
>> I am actually surprised you can reach 8 Mpps with so many cache line 
>> bouncing around.
>>
>> If you replace the ltb qdisc with standard mq+pfifo_fast, what kind of 
>> throughput do you get ?
>>
> 
> Just tried it using pktgen, we are far from baseline. I can get 13Mpps with 
> 10 threads in my test setup.

This is quite low performance.

I suspect your 10 threads are sharing a smaller number of TX queues perhaps ?