Re: [PATCH v9 2/5] perf: arm_spe: Add support for filtering on data source

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Oct 29, 2025 at 03:46:02PM +0000, James Clark wrote:
> SPE_FEAT_FDS adds the ability to filter on the data source of packets.
> Like the other existing filters, enable filtering with PMSFCR_EL1.FDS
> when any of the filter bits are set.
> 
> Each bit maps to data sources 0-63 described by bits[0:5] in the data
> source packet (although the full range of data source is 16 bits so
> higher value data sources can't be filtered on). The filter is an OR of
> all the bits, so for example clearing bits 0 and 3 only includes packets
> from data sources 0 OR 3.
> 
> Invert the filter given by userspace so that the default value of 0 is
> equivalent to including all values (no filtering). This allows us to
> skip adding a new format bit to enable filtering and still support
> excluding all data sources which would have been a filter value of 0 if
> not for the inversion.

So from that I'm reading the config4 field will only have like 16 bits,
but here:

> +#define ATTR_CFG_FLD_inv_data_src_filter_CFG	config4	/* inverse of PMSDSFR_EL1 */
> +#define ATTR_CFG_FLD_inv_data_src_filter_LO	0
> +#define ATTR_CFG_FLD_inv_data_src_filter_HI	63

you claim all 64 bits.

Also, afaict:

  #define ATTR_CFG_FLD_min_latency_CFG            config2 /* PMSLATFR_EL1.MINLAT */
  #define ATTR_CFG_FLD_min_latency_LO             0
  #define ATTR_CFG_FLD_min_latency_HI             11

Still has more than 16 bits left.


So why exactly are we needing config4? Can we please get a more solid
argument?