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

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Message-ID: <91fc642f-6447-4863-a182-388591cc1cc0@gmail.com>
Date:   Wed, 8 Jul 2020 17:08:12 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "YU, Xiangning" <xiangning.yu@...baba-inc.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 2/2] net: sched: Lockless Token Bucket (LTB)
 qdisc



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.

> 
> 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 ?