Re: [Qemu-devel] [RFC v2 00/11] cpu-exec: Safe work in quiescent state

["Alex Bennée" <alex.bennee@linaro.org>]

Sergey Fedorov <sergey.fedorov@linaro.org> writes:

> From: Sergey Fedorov <serge.fdrv@gmail.com>
>
> Hi,
>
> This is a v2 of the RFC series [3] that was a follow-up for a discussion
> on the subject [1]. This is sill marked as FRC becuse it laks bsd-user
> support.

Given the maintenance state of BSD I'm not sure how important this is. I
assume the exclusive handling will be pretty much the same though.

>
> Basically, this series suggests a way to perform some operations in
> quiescent state. The goal is to implement such a mechanism which can be
> used for safe translation buffer flush in multi-threaded user-mode
> emulation (and later in MTTCG) and merge it into mainline as soon as
> possible.
>
> This series is a more elaborated version of the original series since
> there was some positive feedback and I'd appreciate some comments from
> maintainers this time.
>
> The first two patches are some useful tweak from Alex's MTTCG trees.
>
> The patches 3 through 8 are arrangements for the patch 9 which adds
> support for CPU work in linux-user. This wouldn't make any sense without
> the patch 10 which is the subject matter of this series. Although there
> is nothing special to do in case of single-threaded round-robin CPU loop
> of current system-mode emulation to ensure quiescent state, that is
> shown in the patch 10, how it would look like in MTTCG. The last patch
> actually employs this new mechanism making translation buffer flush
> thread safe.
>
> The considerations on expensiveness of work item dynamic allocation [2]
> was not taken into account. I'll just mention here that the desired
> effect can be achieved by either using dynamic arrays for CPU work
> queues or making queue_work_on_cpu() from the patch 3 a public interface
> thus allowing to use preallocated work items.
>
> I would like your comments in order to produce something upstreamable
> quickly!
>
> This series is available at a public git repository:
>
>     https://github.com/sergefdrv/qemu.git safe-cpu-work-v2
>

I've finished by review pass now. If Sergey doesn't get a chance to
re-spin before he moves onto other things I'll pick the series up.

--
Alex Bennée