Re: [Qemu-devel] Summary MTTCG related patch sets

[Mark Burton]

Huge thanks Alex, really good summary
Cheers
Mark.

> On 20 Jul 2015, at 18:17, Alex Bennée <address@hidden> wrote:
> 
> Hi,
> 
> Following this afternoons call I thought I'd summarise the state of the
> various patch series and their relative dependencies. We re-stated the
> aim should be to get what is up-streamable through the review process
> and heading for merge so the delta for a full working MTTCG can be as
> low as possible. There was some concern about the practicality of
> submitting patches where the full benefit will not be seen until MTTCG
> is finally merged.
> 
> On the patch submission note could I encourage posting public git trees
> along with the patches for ease of review?
> 
> BQL lock breaking patches, Paolo/Jan
>  - required for working virt-io in MTTCG
>  - supersedes some of Fred's patches
>  - merged upstream as of -rc0
> 
> TCG async_safe_work, Fred
>  - http://git.greensocs.com/fkonrad/mttcg.git async_work_v3
>  - address@hidden
>  - split from earlier MTTCG patch series
>  - needed for cross-cpu sync mechanism for main series and slow-path
>  - candidate for upstreaming, but only MTTCG uses for now?
> 
> Slow-path for atomic instruction translation, Alvise
>  - address@hidden
>  - Needs re-basing to use TCG async_safe_work
>  - Earlier part of series (pre MTTCG) could be upstreamed as is
>  - Concern about performance impact in non-MTTCG scenarios
>  - Single CPU thread impact may be minimal with latest version, needs
>  benchmarking
>  - Also incomplete backend support, would BACKEND_HAS_LLSC_OPS be
>  acceptable to maintainers while support added by more knowledgable
>  backend people for non-x86/arm backends?
> 
> Multi-threaded TCG V6, Fred
>  - address@hidden:fkonrad/mttcg.git branch multi_tcg_v6
>  - address@hidden
>  - Needs re-basing on top of latest -rc (BQL breaking)
>  - Contains the rest of the MTTCG work (tb locking, tlb stuff etc)
>  - Currently target-arm only, other builds broken
> 
> As far as balancing the desire to get things upstreamed versus having a
> stable base for testing I suggest we try an approach like this:
> 
>  - select the current upstream -rc as the common base point
>  - create a branch from -rc with:
>    - stuff submitted for upstream (reviewed, not nacked)
>    - doesn't break any tree
>    - has minimal performance impact 
> 
> Then both Fred and Alvise could base their trees of this point and we
> aim to rebase onto a new branch each time the patches get merged into a
> new upstream RC. The question then become how to deal with any
> cross-dependencies between the slow-path and the main MTTCG branches?
> 
> I suspect the initial common branch point would just be
> 2.4.0-rc1+safe_async.
> 
> Does that sound workable?
> 
> -- 
> Alex Bennée


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        mark.burton