Noah Meyerhans <noahm@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