Re: [PATCH 0/3] qemu: add support for the SCHED_DEADLINE scheduling policy

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On 8/1/22 19:11, Sasha Algisi wrote:
> Hello everyone,
> 
> This patchset aims at adding support for the SCHED_DEADLINE Linux
> scheduling policy for vcpus, io-threads and emulator processes.
> 
> In fact, libvirt currently supports SCHED_OTHER, SCHED_BATCH,
> SCHED_IDLE, SCHE_FIFO and SCHED_RR, but not SCHED_DEADLINE.
> SCHED_DEADLINE is a policy implementing an algorithm originating from
> the real-time scheduling community, but it can be useful outside of
> the real-time computing field as well.
> 
> It allows one to set a specific amount of CPU time that a task should
> receive with a given periodicity, and withing a certain deadline.
> E.g., task t should be scheduled at least for 50 ms every 100 ms. To
> achieve this, it needs 3 parameters: runtime, deadline and period
> (although period can just be equal to deadline, which is what happens
> automatically if one sets period=0). It must always hold that:
> runtime <= deadline <= period (and this is enforced by the kernel,
> but checks are included in the patches, so that meaningful and easy
> to interpret error messages can be printed to the user).
> 
> More info on SCHED_DEADLINE are available here:
> 
> https://docs.kernel.org/scheduler/sched-deadline.html
> 
> The interface will look like this, e.g., for setting SCHED_DEADLINE
> as a policy for 3 (0-2) vcpus, with runtime = 10000000, deadline =
> 15000000 and period = 20000000:
> 
>   <cputune>
>     ...
>     <vcpusched vcpus="0-2" scheduler="deadline" runtime="10000000"
>      deadline="15000000" period="20000000"/>
>     ...
>   </cputune>
> 
> This a link to a branch containing the patches:
> 
> https://gitlab.com/Algisi-00/libvirt/-/tree/sched-deadline
> 
> And this is the link to results of running the CI on such branch:
> 
> https://gitlab.com/Algisi-00/libvirt/-/pipelines/601795712
> 
> Note that the jobs that are failing are also failing in the exact
> same way without these patches applied.
> 
> Feedback is welcome and very much appreciated.
> 
> Thanks and regards.
> 
> Sasha Algisi (3):
>   virprocess: define sched_attr and sched_setattr
>   virprocess: add the SCHED_DEADLINE scheduling policy
>   domain_conf: add SCHED_DEADLINE support in the XML configuration
> 
>  NEWS.rst                          |   5 ++
>  docs/formatdomain.rst             |  16 +++-
>  src/ch/ch_process.c               |   3 +-
>  src/conf/domain_conf.c            |  52 +++++++++++--
>  src/conf/domain_conf.h            |   3 +
>  src/conf/schemas/domaincommon.rng |  16 ++++
>  src/qemu/qemu_process.c           |   8 +-
>  src/util/virprocess.c             | 123 +++++++++++++++++++++++++++++-
>  src/util/virprocess.h             |   6 +-
>  9 files changed, 216 insertions(+), 16 deletions(-)
> 

Hey, the code looks good. However, we require that the code compiles
after each patch, which is not the case with your series. The reason for
our requirement is simple: easy git bisect. Therefore, it's okay if
feature does not work until the very last commit. We often have
patches/commits that work gradually towards grand finale.

Can you please fix that in v2?

Michal




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