On Tue, May 20, 2025 at 04:00:59PM +0100, James Clark wrote: > On 20/05/2025 2:46 pm, Leo Yan wrote: > > On Tue, May 06, 2025 at 12:41:39PM +0100, 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 setting bits 0 and 3 filters packets from > > > data sources 0 OR 3. > > > > As Arm ARM says: > > > > 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. > > > > We need extra handling for this configuration (0b0 means filtering, > > 0b1 means no affaction): > > > > - By default, the driver should set all bits in the 'data_src_filter' > > field. > > > > - The perf tool needs an extra patch in userspace to initialize all > > bits in config4 unless user specify other values. > > > > Did you take into account PMSFCR_EL1.FDS being set automatically? Good point. TBH, I did not give it enough consideration until your remdinding, but let me elaborate on why I suggested the approach above. > I think the wording is slightly confusing but I tested it on the model and it works. > > If PMSFCR_EL1.FDS == 0 then PMSDSFR_EL1 does nothing, and if the data source > filter isn't set by the user then FDS isn't set so there's no need to set > all the bits in the filter to 1. Once the user asks for any filter then we > set FDS, at which point it's whatever filter they asked for. They can set > all the bits if they want, or just one. > > This is same way PMSFCR_EL1.FT already works. If the user asks for any > filter then it's set automatically, but we don't allow the user to ask for > "no filters" but with FT set. > > So the only thing we can't do is filter out samples with _any_ data source. > Which would be PMSFCR_EL1.FDS == 1 and PMSDSFR_EL1 == 0. But I don't think > that's useful, and there are other filters to get you all or most of the way > there. My suggestion is coming for handling the case you mentioned. Let us see the combinations: PMSFCR_EL1.FDS == 0 PMSDSFR_EL1 == 0xFFFF,FFFF,FFFF,FFFF No filtering on data source PMSFCR_EL1.FDS == 1 PMSDSFR_EL1 == 0xFFFF,FFFF,FFFF,FFFF No filtering on data source PMSFCR_EL1.FDS == 0 PMSDSFR_EL1 == 0x0 No filtering on data source PMSFCR_EL1.FDS == 1 PMSDSFR_EL1 == 0x0 Filtering on all data source If 'PMSFCR_EL1.FDS == 0 and PMSDSFR_EL1 == 0xFFFF,FFFF,FFFF,FFFF' is initialized state, when a user set all bits to '1' for the data source filter, then no matter we enable or disable FDS bit, it can work as expected for disabling filtering. 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. How about you think? Thanks, Leo
