William Tu d265929930
netfilter: nf_conncount: reduce unnecessary GC ...
Currently nf_conncount can trigger garbage collection (GC)
at multiple places. Each GC process takes a spin_lock_bh
to traverse the nf_conncount_list. We found that when testing
port scanning use two parallel nmap, because the number of
connection increase fast, the nf_conncount_count and its
subsequent call to __nf_conncount_add take too much time,
causing several CPU lockup. This happens when user set the
conntrack limit to +20,000, because the larger the limit,
the longer the list that GC has to traverse.
The patch mitigate the performance issue by avoiding unnecessary
GC with a timestamp. Whenever nf_conncount has done a GC,
a timestamp is updated, and beforce the next time GC is
triggered, we make sure it's more than a jiffies.
By doin this we can greatly reduce the CPU cycles and
avoid the softirq lockup.
To reproduce it in OVS,
$ ovs-appctl dpctl/ct-set-limits zone=1,limit=20000
$ ovs-appctl dpctl/ct-get-limits
At another machine, runs two nmap
$ nmap -p1- <IP>
$ nmap -p1- <IP>
Signed-off-by: William Tu <u9012063@gmail.com >
Co-authored-by: Yifeng Sun <pkusunyifeng@gmail.com >
Reported-by: Greg Rose <gvrose8192@gmail.com >
Suggested-by: Florian Westphal <fw@strlen.de >
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org >
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d265929930