Re: [PATCH v3 4/7] perf arm-spe: Use metadata to decide the data source feature

[Leo Yan]

On 10/10/24 14:53, James Clark wrote:

[...]

> > +static bool arm_spe__is_common_ds_encoding(struct arm_spe_queue *speq)
> > +{
> > +     struct arm_spe *spe = speq->spe;
> > +     bool is_in_cpu_list;
> > +     u64 *metadata = NULL;
> > +     u64 midr = 0;
> > +
> > +     /*
> > +      * Metadata version 1 doesn't contain any info for MIDR.
> > +      * Simply return false in this case.
> > +      */
> > +     if (spe->metadata_ver == 1) {
> > +             pr_warning_once("The data file contains metadata version 1, "
> > +                             "which is absent the info for data source. "
> > +                             "Please upgrade the tool to record data.\n");
> > +             return false;
> > +     }
> > +
> > +     /* CPU ID is -1 for per-thread mode */
> > +     if (speq->cpu < 0) {
> > +             /*
> > +              * On the heterogeneous system, due to CPU ID is -1,
> > +              * cannot confirm the data source packet is supported.
> > +              */
> > +             if (!spe->is_homogeneous)
> > +                     return false;
>
> Technically you could look at timestamps and context switches to find
> the CPU for non-homogeneous per-thread mode. But it's such an edge case
> I'm not sure it's even worth leaving a TODO for.

Good point. Let’s bear the idea in mind in case we need it later.

Thanks,
Leo