Messages in this thread | | | Subject | Re: [PATCH v4 00/24] x86/resctrl: Merge the CDP resources | From | James Morse <> | Date | Tue, 15 Jun 2021 17:48:25 +0100 |
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Hi Reinette,
On 15/06/2021 17:16, Reinette Chatre wrote: > On 6/14/2021 1:09 PM, James Morse wrote: >> This series re-folds the resctrl code so the CDP resources (L3CODE et al) >> behaviour is all contained in the filesystem parts, with a minimum amount >> of arch specific code.
[..]
>> This series collapses the CODE/DATA resources, moving all the user-visible >> resctrl ABI into what becomes the filesystem code. CDP becomes the type of >> configuration being applied to a cache. This is done by adding a >> struct resctrl_schema to the parts of resctrl that will move to fs. This >> holds the arch-code resource that is in use for this schema, along with >> other properties like the name, and whether the configuration being applied >> is CODE/DATA/BOTH. >> >> This lets us fold the extra resources out of the arch code so that they >> don't need to be duplicated if the equivalent feature to CDP is missing, or >> implemented in a different way.
[...]
>> This series is based on v5.12-rc6, and can be retrieved from: >> git://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/resctrl_merge_cdp/v4
> For the most part I think this series looks good. The one thing I am concerned about is > the resctrl user interface change. On a system that supports L3 CDP there is a visible > change when CDP is not enabled: > > Before this series: > # cat schemata > L3:0=fffff;1=fffff > > After this series: > # cat schemata > L3:0=fffff;1=fffff
Hmm, I thought I'd fixed this with v2, ... I see this is subtly different.
This could be tweaked by getting schemata_list_add() to include the length of the longest suffix if the resource supports CDP, but its not enabled. (Discovering that means cdp_capable moves to be something the 'fs' bits of resctrl can see.)
I'm a little nervous 'adding 4 spaces' because user-space expects them. (I agree if it breaks user-space it has to be done). I guess this is the problem with string parsing as part of the interface!
I assume that in the (distant) future having CDP capable resources with names more than 2 characters isn't going to be a problem. (I don't have an example)
> There are a few user space tools that parse the resctrl schemata file and it may be easier > to keep the interface consistent than to find and audit them all to ensure they will keep > working.
> Apart from that, I do think that the dmesg change that Babu pointed out deserves a mention > in the cover letter. I agree with your response in this regard but this is indeed a user > visible change and if anybody has issue with that then mentioning it in the cover letter > will hopefully catch it sooner.
Ah, okay.
> A heads-up is that there are some kernel-doc fixups in the works that will conflict with > your series. You yourself fix at least one of these kernel-doc issues in this series - the > description of mbm_width in the first patch. I will ask the submitter of the kernel-doc > fixups to use your text to help with the merging.
Please point me at something to rebase onto! (as far as I can see, tip/x86/cache hasn't moved)
> Finally, I did catch a few typos that I will respond to individually.
Thanks!
James
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