RE: [PATCH RFC] soc: fujitsu: Add cache driver code

["tan.shaopeng@fujitsu.com" <tan.shaopeng@fujitsu.com>]

Hi James Morse

> On 31/03/2021 09:52, tan.shaopeng@fujitsu.com wrote:
> >>> Given that all of this is outside of the scope of the architecture,
> >>> I don't think that arch/arm64/ is the right place for it. Perhaps
> >>> this would fit into the resctrl rework that James has been doing for
> MPAM?
> >>
> >> Indeed, that sounds like a good starting point. I don't understand
> >> enough about either of the two to be sure, but it sounds like there
> >> is some overlap in functionality, and ideally we would have one user
> >> interface that can deal with all the hardware implementations (intel, arm,
> fujitsu and any future ones).
> 
> > According to my study, it seems possible to add A64FX's sector cache
> > function to resctrl.
> 
> I think this depends on whether it maps to one of Intel RDT's existing schema.
> While adding new ones looks easy, it is bad for user-space as they are not
> portable between machines that support resctrl.

Thanks for your advice, I will try finding a way to add
the sector cache function in resctrl by using existing schema.

> > I heard you are working on resctrl rework for MPAM , but I cannot find
> > related patches on ML archive. Therefore, I would like to know the
> > status about MPAM support.
> 
> Its about five or six series that refactor resctrl inside arch/x86 to have a clear
> boundary between arch-specific code and the resctrl code that implements the
> filesystem, then pull it out to /fs/ and build the MPAM driver to make it work for
> arm64.
> 
> Unfortunately, its rather large (>100 patches), so will take some time to be
> reviewed.
> 
> 
> > (1) I think the first step is to support resctrl for ARM arch.
> >    Have you finished the work of arm support and when will you release it?
> 
> No-one wants a second copy of the code to implement resctrl, as this will
> introduce subtle bugs that user-space would have to work around, and make it
> harder to merge later.
> 
> The first step is to refactor the arch/x86 implementation of resctrl so that the
> parts that are visible to user-space can be moved somewhere that is common
> to multiple architectures.
> 
> I've posted the next chunk of that work here:
> https://lore.kernel.org/lkml/20210312175849.8327-1-james.morse@arm.com/
> 
> > (2) When will you release MPAM patch?
> 
> The latest complete version of the tree is here:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/log/?h=mpa
> m/snapshot/feb
> 
> It is over a year old, and has plenty of bugs.
> 
> I hope to push a newer version of the branch once I have a complete copy of the
> tree that has been tested, and is based on the current version of the ACPI table.

Thanks for your information. Let me see the patch.

Thanks, 
Tan Shaopeng
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