Re: [RFC PATCH v0.1 4/9] sched/umcg: implement core UMCG API

[Andy Lutomirski]

On Thu, May 20, 2021 at 11:36 AM Peter Oskolkov <posk@xxxxxxxxxx> wrote:
>
> Implement version 1 of core UMCG API (wait/wake/swap).
>
> As has been outlined in
> https://lore.kernel.org/lkml/20200722234538.166697-1-posk@xxxxxxx/,
> efficient and synchronous on-CPU context switching is key
> to enabling two broad use cases: in-process M:N userspace scheduling
> and fast X-process RPCs for security wrappers.
>
> High-level design considerations/approaches used:
> - wait & wake can race with each other;
> - offload as much work as possible to libumcg in tools/lib/umcg,
>   specifically:
>   - most state changes, e.g. RUNNABLE <=> RUNNING, are done in
>     the userspace (libumcg);
>   - retries are offloaded to the userspace.

Do you have some perf numbers as to how long a UMCG context switch
takes compared to a normal one?

--Andy