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d265929930
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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.