On Thu, 2015-11-12 at 14:13 +0100, Quentin Deldycke wrote: > Source: linux > Severity: wishlist > > Dear Maintainer, > > Could you please enable kernel options CONFIG_NO_HZ_FULL, > CONFIG_RCU_NOCB_CPU and CONFIG_RCU_NOCB_CPU_NONE. > > As explained in: https://www.kernel.org/doc/Documentation/timers/NO_HZ.txt > > This options: > - Don't modify default kernel behavior > - Enable kernel command line nohz_full to enable tickless cpus > - Enable kernel command line rcu_nocbs to offload rcu callbacks > > The combination of these parameters + cpu-pinning of virtual machines > greatly improve performance. > It also reduces latency in these virtual machines as the host system > doesn't try to use it. (if your cgroup is correctly made) [...] But for other configurations it is worse: config NO_HZ_FULL bool "Full dynticks system (tickless)" ... This is implemented at the expense of some overhead in user <-> kernel transitions: syscalls, exceptions and interrupts. Even when it's dynamically off. Say N. I think we should enable this for the rt featureset when it's next available, but not by default. Ben. -- Ben Hutchings Logic doesn't apply to the real world. - Marvin Minsky
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