# Re: \[RFC PATCH v0.1 0/9\] UMCG early preview/RFC patchset

- From: Peter Oskolkov \<hidden\>
- Date: 2021-05-21 19:14:11 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/05/1387946
- Thread: https://ratatoskr.run/linux-api/2021/05/1387946/t.md

```text
On Fri, May 21, 2021 at 11:44 AM Andrei Vagin [ref] wrote:
>
>
>
> On Thu, May 20, 2021 at 11:36 AM Peter Oskolkov [ref] wrote:
>>
>> As indicated earlier in the FUTEX_SWAP patchset:
>>
>> https://lore.kernel.org/lkml/20200722234538.166697-1-posk@posk.io/
>
>
> Hi Peter,
>
> Do you have benchmark results? How fast is it compared with futex_swap and the google switchto?

Hi Andrei,

I did not run benchmarks on the same machine/kernel, but umcg_swap
between "core" tasks (your use case for gVisor) should be somewhat
faster than futex_swap, as there is no reading from the userspace and
no futex hash lookup/dequeue ops; umcg_swap should be slower than
switchto_switch because umcg_swap does go through ttwu+schedule, which
switchto_switch bypasses.

I expect that if UMCG is merged in a form similar to what I posted, we
will explore how to make UMCG context switches faster in later
patches.

Thanks,
Peter

>
> Thanks,
> Andrei
```