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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v7 07/12] xen: enable Dom0 to use SVE feature
> On 23 May 2023, at 12:53, Jan Beulich <jbeulich@xxxxxxxx> wrote: > > On 23.05.2023 13:50, Luca Fancellu wrote: >>> On 23 May 2023, at 11:31, Jan Beulich <jbeulich@xxxxxxxx> wrote: >>> On 23.05.2023 12:21, Luca Fancellu wrote: >>>>> On 23 May 2023, at 11:02, Jan Beulich <jbeulich@xxxxxxxx> wrote: >>>>> On 23.05.2023 09:43, Luca Fancellu wrote: >>>>>> @@ -838,6 +838,22 @@ Controls for how dom0 is constructed on x86 systems. >>>>>> >>>>>> If using this option is necessary to fix an issue, please report a bug. >>>>>> >>>>>> +Enables features on dom0 on Arm systems. >>>>>> + >>>>>> +* The `sve` integer parameter enables Arm SVE usage for Dom0 domain >>>>>> and sets >>>>>> + the maximum SVE vector length, the option is applicable only to >>>>>> AArch64 >>>>>> + guests. >>>>> >>>>> Why "guests"? Does the option affect more than Dom0? >>>> >>>> I used “guests” because in my mind I was referring to all the aarch64 OS >>>> that can be used >>>> as control domain, I can change it if it sounds bad. >>> >>> If you means OSes then better also say OSes. But maybe this doesn't need >>> specifically expressing, by saying e.g. "..., the option is applicable >>> only on AArch64"? Or can a Dom0 be 32-bit on Arm64 Xen? >> >> I think there is no limitation so Dom0 can be 32 bit or 64. Maybe I can say >> “... AArch64 kernel guests.”? > > I'd recommend to avoid the term "guest" when you talk about Dom0 alone. > Commonly "guest" means ordinary domains only, i.e. in particular excluding > Dom0. What's wrong with "AArch64 Dom0 kernels"? Ok works for me, I will use “AArch64 Dom0 kernels", I thought “guests” were a generic category and then we have “privileged guests”, for example Dom0 or driver domain, and “unprivileged guests” like DomUs. > >>>>>> + A value equal to 0 disables the feature, this is the default value. >>>>>> + Values below 0 means the feature uses the maximum SVE vector length >>>>>> + supported by hardware, if SVE is supported. >>>>>> + Values above 0 explicitly set the maximum SVE vector length for >>>>>> Dom0, >>>>>> + allowed values are from 128 to maximum 2048, being multiple of 128. >>>>>> + Please note that when the user explicitly specifies the value, if >>>>>> that value >>>>>> + is above the hardware supported maximum SVE vector length, the >>>>>> domain >>>>>> + creation will fail and the system will stop, the same will occur if >>>>>> the >>>>>> + option is provided with a non zero value, but the platform doesn't >>>>>> support >>>>>> + SVE. >>>>> >>>>> Assuming this also covers the -1 case, I wonder if that isn't a little too >>>>> strict. "Maximum supported" imo can very well be 0. >>>> >>>> Maximum supported, when platforms uses SVE, can be at minimum 128 by arm >>>> specs. >>> >>> When there is SVE - sure. But when there's no SVE, 0 is kind of the implied >>> length. And I'd view a command line option value of -1 quite okay in that >>> case: They've asked for the maximum supported, so they'll get 0. No reason >>> to crash the system during boot. >> >> Ok I see what you mean, for example when Kconfig SVE is enabled, but the >> platform doesn’t >> have SVE feature, requesting sve=-1 will keep the value to 0, and no system >> will be stopped. >> >> Maybe I can say: >> >> “... the same will occur if the option is provided with a positive non zero >> value, >> but the platform doesn't support SVE." > > Right, provided that matches the implementation. Ok I will do the changes, can I retain your R-by? I suppose it covers also documentation right? > > Jan
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