netdev - Re: [PATCH net-next v5 1/5] net/smc: Make smc_tcp_listen

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Date:   Wed, 9 Feb 2022 14:24:15 +0800
From:   "D. Wythe" <alibuda@...ux.alibaba.com>
To:     Karsten Graul <kgraul@...ux.ibm.com>
Cc:     kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next v5 1/5] net/smc: Make smc_tcp_listen_work()
 independent

It is indeed okay to use system_wq at present. Dues to the load 
balancing issues we found, queue_work() always submits tasks to the 
worker on the current CPU. tcp_listen_work() execution once may submit a 
large number of tasks to the worker of the current CPU, causing 
unnecessary pending, even though worker on other CPU are totaly free. I 
was plan to make tcp_listen_work() blocked wait on worker of every CPU, 
so I create a new workqueue, and that's the only reason for it. But this 
problem is not very urgent, and I don't have strong opinion too...


在 2022/2/9 上午1:06, Karsten Graul 写道:
> On 08/02/2022 13:53, D. Wythe wrote:
>> +static struct workqueue_struct	*smc_tcp_ls_wq;	/* wq for tcp listen work */
>>   struct workqueue_struct	*smc_hs_wq;	/* wq for handshake work */
>>   struct workqueue_struct	*smc_close_wq;	/* wq for close work */
>>   
>> @@ -2227,7 +2228,7 @@ static void smc_clcsock_data_ready(struct sock *listen_clcsock)
>>   	lsmc->clcsk_data_ready(listen_clcsock);
>>   	if (lsmc->sk.sk_state == SMC_LISTEN) {
>>   		sock_hold(&lsmc->sk); /* sock_put in smc_tcp_listen_work() */
>> -		if (!queue_work(smc_hs_wq, &lsmc->tcp_listen_work))
>> +		if (!queue_work(smc_tcp_ls_wq, &lsmc->tcp_listen_work))
>>   			sock_put(&lsmc->sk);
> 
> It works well this way, but given the fact that there is one tcp_listen worker per
> listen socket and these workers finish relatively quickly, wouldn't it be okay to
> use the system_wq instead of using an own queue? But I have no strong opinion about that...