Noah Meyerhans <no...@debian.org> writes: > On Fri, Sep 27, 2019 at 01:15:29PM -0700, Flavio Veloso wrote: >> Since linux-image-cloud-* packages are created for cloud environments -- >> read: servers which do not need desktop-level responsiveness --, wouldn't it >> be beneficial to build the kernels with CONFIG_HZ set to 100? >
I wonder if the upstream docstring could be improved, because to my mind 100hz only makes sense for throughput-limited workloads, or for big SMP systems. eg: when you have one 100hz timer running on each of 32 cores the effect on latency is more like a ~3200hz timer than a 100hz one. Also, network latency is a big deal now, so I'm not sure if this docstring is accurate anymore. > For what it's worth, the Amazon Linux 2 4.14.x kernel also ships with > CONFIG_HZ=250. We obviously don't need to use the same settings, but > that kernel specifically targets cloud deployments, and its maintainers > do not see a need to set CONFIG_HZ=100. > > I don't know what considerations were taken into account when choosing > the value for that variable at AWS. > Maybe something like socket activation, subprocess or thread creation latency? Or maybe because it's useful to have a 250hz timer when your vhost only has one vcpu? 'just some non-authoritative thoughts. I'm sure Ben can say for sure :-) Take care! Nicholas
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