From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 02E462F8C5C; Thu, 17 Jul 2025 15:27:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752766038; cv=none; b=BrLGdDohM+hE2wbB7AeR7LV/uTyUUL3nNPD5N23ohQrU4FHsNrcORmwUCv3+pXnS373b3jVrbCaVgBb8AVU/TtSMkRHYJNW4NaRre/M13ZAUodFCLZtA9VNdumoX21MoaYIG3FDzaAx2SxDxEaL70OxshyzgEzCV/xhODCaYBv8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752766038; c=relaxed/simple; bh=4yydri2iXJ+vkt3rGzpbKbnKbfLngsgnmN/hlvqV+sM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eL4zG9cd/B9R35Feuy3eJAndRU4s2ZV2kGr+TKXXTE/+zGV68ysIvr9JsjVotaDNO1TJMOmx9puk1tv+Jno8W/oYxIHORBOfb2wMr+uSdEKGWBceXNlnxWwVumueWnL0VWRDyfEU+HY5ED7buIptL9hHSzoxbI1EfKFtmUn+FzM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Jkc2HIzl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Jkc2HIzl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B64C4C4CEE3; Thu, 17 Jul 2025 15:27:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1752766037; bh=4yydri2iXJ+vkt3rGzpbKbnKbfLngsgnmN/hlvqV+sM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Jkc2HIzlh/f85sSERCDk6FnHc0o7b/fmOkjr6/ic6/EdFaEA6woHqSEIO4UapszO3 e44POPFs96UF2owJnF1avPhvQuRZb5ouwef1zHHAjIy52Oz0BirO81qvr+Eh2YT8b6 8B8xIrTOYVNMboxBpbEH4wB1OHUbsvjAVNYlwhxBEM/r8CJNP34/vxr9JgvjPrkoca 9gDVTA8RV8ohYM5nBBQ4rKUGFvm1jVOwuhO4KfdUicfQSuM29KK4mSro9vBNXeCaXu 5/ZyE4QwYAq1ZyS+4u2iCDD0/ofDKmH9rlEu+Yb7H+ZnnDzW+otjrPKMmLW+4mE4YC FCYvQo3eJAbIA== Date: Thu, 17 Jul 2025 16:27:10 +0100 From: Will Deacon To: James Clark Cc: Catalin Marinas , Mark Rutland , Jonathan Corbet , Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , leo.yan@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev Subject: Re: [PATCH v3 07/10] perf: arm_spe: Add support for filtering on data source Message-ID: References: <20250605-james-perf-feat_spe_eft-v3-0-71b0c9f98093@linaro.org> <20250605-james-perf-feat_spe_eft-v3-7-71b0c9f98093@linaro.org> <7f51d4f9-7e08-49b5-ab43-8bc765bb2ca8@linaro.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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 > > > > > > 0b0 If PMSFCR_EL1.FDS is 1, do not record load operations that have > > > bits [5:0] of the Data Source packet set to . > > > > > > 0b1 Load operations with Data Source 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@linaro.org/ > > > > > > 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