On Thu, Jul 17, 2025 at 04:16:32PM +0100, James Clark wrote: > > > On 17/07/2025 3:29 pm, Will Deacon wrote: > > On Tue, Jul 15, 2025 at 02:04:18PM +0100, James Clark wrote: > > > On 14/07/2025 3:04 pm, Will Deacon wrote: > > > > On Thu, Jun 05, 2025 at 11:49:05AM +0100, James Clark wrote: > > > > > @@ -406,6 +416,9 @@ static u64 arm_spe_event_to_pmsfcr(struct perf_event *event) > > > > > if (ATTR_CFG_GET_FLD(attr, inv_event_filter)) > > > > > reg |= PMSFCR_EL1_FnE; > > > > > + if (ATTR_CFG_GET_FLD(attr, data_src_filter)) > > > > > + reg |= PMSFCR_EL1_FDS; > > > > > > > > Is the polarity correct here? The description of PMSDSFR_EL1.S<m> suggests > > > > that setting bits to 1 _excludes_ the FDS filtering. > > > > > > > > > > Setting filter bits to 1 means that samples matching are included. Setting > > > bits to 0 means that they are excluded. And PMSFCR_EL1.FDS enables filtering > > > as a whole, so if the user sets any filter bit to 1 we want to enable > > > filtering: > > > > > > PMSDSFR_EL1.S<m> > > > > > > 0b0 If PMSFCR_EL1.FDS is 1, do not record load operations that have > > > bits [5:0] of the Data Source packet set to <m>. > > > > > > 0b1 Load operations with Data Source <m> are unaffected by > > > PMSFCR_EL1.FDS. > > > > > > I think it's all the right way around and it ends up being the same as the > > > other filters in SPE. Because we're using any bit being set to enable the > > > filtering, the only thing you can't do is enable filtering with a 0 filter, > > > but I didn't think that was useful. See the previous discussion on this > > > here: > > > https://lore.kernel.org/all/5752f039-51c1-4452-b5df-03ff06da7be3@xxxxxxxxxx/ > > > > > > Reading the "Data source filtering" section in the docs change at the end > > > might help too. > > > > Sorry, but I still don't get it :/ > > > > afaict, if any of the bits in 'data_src_filter' are _zero_ then we > > should set PMSFCR_EL1.FDS. That also means that a mask of zero means all > > loads are filtered, which is what the architecture says and is what we > > should provide to userspace. > > > > Will > > We'd have to add another format flag to enable data source filtering then, > because otherwise the default would be zero and people's samples would > disappear. > > But the only use cases I could think of were more like "I want to see > samples from data source 1": > > -e arm_spe/data_src_filter=0x1/ > > Or "I want to see all data sources except 1": > > -e arm_spe/data_src_filter=0xfffffffe/ > > Filtering out all samples with any data source didn't seem to make sense to > me, and I think you can already do that with the other filters (remove loads > etc). > > It would be a shame to be inconsistent and to add an enable flag just for > that one case because the other filters in SPE are auto enabled for non-zero > values. Although to be fair for PMSFCR.FT and others, zero filters are > explicitly not allowed: > > If this field is set to 1 and the PMSFCR_EL1.{ST, LD, B} bits are all > set to zero, it is CONSTRAINED UNPREDICTABLE whether no samples are > recorded or the PE behaves as if PMSFCR_EL1.FT is set to 0 > > Seems like FDS doesn't end up as neat as the others, but IMO I can't see > anyone needing a zero filter. I did discuss it with Leo and we decided that > we could always add the enable flag at a later date if a use case turned up > and it wouldn't be a breaking change. > > But if you think it's there so it should be exposed I can add it. What about if we expose the inverse of PMSDSFR_EL1 to userspace instead? Will
