Re: [RFC PATCH v2 1/2] tick/nohz: Add a policy dependency for full dynticks

[Frederic Weisbecker <frederic@kernel.org>]

Le Thu, Oct 29, 2026 at 02:41:28PM +0800, Peng Wang a écrit :
> Hi Frederic,
> 
> > Do you mean that your database runs better when hosts CPUs are in nohz_full?
> 
> Yes. In our database tests, suppressing the host's non-idle
> periodic tick improved performance, with the rest of the host
> configuration unchanged.

Out of curiosity, for such database tests, only the host tick is off, not the guest
tick, right?

> > But how does this new interface help? Ie: why is it worse to have all CPUs in
> 
> The tick policy itself can therefore affect guest performance.
> A large host runs VMs for many customers with different workloads.
> Customers create and release VMs independently, so the same host
> CPU can be reassigned to a different workload while other VMs
> remain running.
> 
> We want to choose whether to retain the non-idle tick or allow its
> suppression for the workload currently assigned to each CPU, and
> revisit that choice when the CPU is reassigned. Per-CPU control
> lets us do this without rebooting or taking CPUs offline.

Ok in that case, do you know about the current work in progress
to make nohz_full opt-able through cpusets? It implies taking the
target CPUs offline shortly but the policy is to be setup before VM
is launched, right?

Thanks.

-- 
Frederic Weisbecker
SUSE Labs