Re: [PATCH 07/10] perf: arm_spe: Add support for filtering on data source

[James Clark <james.clark@linaro.org>]

On 20/05/2025 5:22 pm, Leo Yan wrote:
> On Tue, May 20, 2025 at 05:10:03PM +0100, Leo Yan wrote:
> 
> [...]
> 
>> If 'PMSFCR_EL1.FDS == 0 and PMSDSFR_EL1 == 0x0' is the init state, as
>> you said, when user passed 0xFFFF,FFFF,FFFF,FFFF for data filter, we
>> cannot distinguish it from the init state, as a result, we will fail
>> to handle this case.
> 
> Correct a typo. The case above, it means "when a user passes 0x0 for
> data source filter ....".
> 
> Sorry for spamming.
> 
> Leo

I'm thinking I'd rather leave it consistent with PMSFCR_EL1.FT and 
automatically enable PMSFCR_EL1.FDS for any non zero data-source filter.

This means we don't need a tool change to set some other flag when a 
filter is provided (even if it's zero) and it's much simpler. It also 
doesn't prevent the possibility of adding the enable flag in the future 
if someone comes out with a need for it, but I don't think it needs to 
be done now. TBH I can't imagine a case where someone would want to 
filter out any samples that have any data source. Surely you'd only be 
looking for a selected set of data sources, or no filtering at all.