netdev - Long delay on estimation_timer causes packet latency

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Date:   Thu, 16 Apr 2020 15:00:53 -0700
From:   yunhong-cgl jiang <xintian1976@...il.com>
To:     horms@...ge.net.au, ja@....bg
Cc:     netdev@...r.kernel.org, lvs-devel@...r.kernel.org,
        Yunhong Jiang <yunhjiang@...y.com>
Subject: Long delay on estimation_timer causes packet latency

Hi, Simon & Julian,
	We noticed that on our kubernetes node utilizing IPVS, the estimation_timer() takes very long (>200sm as shown below). Such long delay on timer softirq causes long packet latency.  

          <idle>-0     [007] dNH. 25652945.670814: softirq_raise: vec=1 [action=TIMER]
.....
          <idle>-0     [007] .Ns. 25652945.992273: softirq_exit: vec=1 [action=TIMER]

	The long latency is caused by the big service number (>50k) and large CPU number (>80 CPUs),

	We tried to move the timer function into a kernel thread so that it will not block the system and seems solves our problem. Is this the right direction? If yes, we will do more testing and send out the RFC patch. If not, can you give us some suggestion?

Thanks
—yunhong