Messages in this thread | | | Subject | Re: [PATCH v2 3/4] perf: add arm64 smmuv3 pmu driver | From | Robin Murphy <> | Date | Tue, 11 Sep 2018 11:24:54 +0100 |
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On 10/09/18 17:37, Shameerali Kolothum Thodi wrote: [...] >>> @@ -0,0 +1,838 @@ >>> +// SPDX-License-Identifier: GPL-2.0+ >>> +/* Copyright (c) 2017 The Linux Foundation. All rights reserved. >>> + * >>> + * This program is free software; you can redistribute it and/or >>> +modify >>> + * it under the terms of the GNU General Public License version 2 and >>> + * only version 2 as published by the Free Software Foundation. >>> + * >>> + * This program is distributed in the hope that it will be useful, >>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of >>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the >>> + * GNU General Public License for more details. >> >> You don't really need to add the license text as well as SPDX. Except for the fact >> that in this case they don't match - which is it? > > Right. I will stick to SPDX-License-Identifier: GPL-2.0+
My question there is about the "+" - the license of the original patch was GPL-2.0, and I'm not sure about the legitimacy of quietly changing it to 2.0-or-later, especially without any visible agreement from previous contributors.
[...] >> Also, how relevant is it going to be for future DT support? We don't really want >> too many artificial dependencies on the way ACPI support happens to currently >> be implemented. > > Sorry, it's not clear to me what is proposed here as far as naming the PMU is > concerned. Please see below as well.
Here I mean whether pdev->id is meaningful for OF platform devices in the same way as for IORT devices in terms of uniqueness - it may well be, but if it isn't then we should find a better alternative.
>>> +out: >>> + kfree(temp); >>> + return ret; >>> +} >>> + >>> + >>> +static char *smmu_pmu_assign_name(struct smmu_pmu *pmu) { >>> + unsigned long id; >>> + struct device *smmu, *dev = pmu->dev; >>> + char *s_name = NULL, *p_name = NULL; >>> + >>> + smmu = iort_find_pmcg_ref_smmu(dev); >>> + if (smmu) { >>> + if (!smmu_pmu_get_dev_id(dev_name(smmu), &id)) >>> + s_name = kasprintf(GFP_KERNEL, >> "arm_smmu_v3_%lu", id); >>> + } >>> + >>> + if (!s_name) >>> + s_name = kasprintf(GFP_KERNEL, "arm_smmu_v3"); >> >> As I touched on before, I think it's worth generalising this from the start, and >> trying to resolve the component reference to a struct device rather than >> IORT/SMMU specific internals. However it also occurs to me that maybe this >> isn't as important as it first seemed - since the auto-numbered ID doesn't >> actually say which PMCG is which, the only way for the user to actually identify >> which PMU is the correct one to count events for a particular endpoint is still to >> grovel up the base address, so as long as the PMU name uniquely correlates to >> the PMCG device, I'm not sure anything really matters beyond that. > > So If I understand this correctly, > > iort_find_pmcg_ref_smmu() should be something like iort_find_pmcg_ref() > which returns the associated struct device for the ref node and then, pmu is > named as, > > arm_smmu_v3_x_pmcg_y > nc_dev_name_x_pmcg_y > pciXXXX_pmcg_y (It’s a bit tricky for RC as we will end up with struct pci_bus) > > (where x and y are auto ids) > > Please let me know if this is what is proposed here.
That's more or less what I was angling at, but as mentioned I realise it's fundamentally flawed (looking back at the original thread, I see it was me that proposed the idea, quelle suprise!)
Say you want to count events on one particular stream ID - how do you determine which of "arm_smmu_v3_0_pmcg_0" to "arm_smmu_v3_0_pmcg_6" represents the actual TBU that can see that SID? Sure, you have a *bit* more information than if they were just named, say, "arm_pmcg_0" to "arm_pmcg_6", but it's not actually *useful* information because those IDs only really represent the probe order, and that depends entirely on the IORT/DT order and whatever Linux felt like doing.
Thus if going to all this effort to compose a complex name still doesn't actually help the user in most cases, is it worth it? I'm starting to think not.
> It is possible to include the pmcg base address instead of the auto-numbered id > as proposed in v1 series.
That's probably the most robust option for now unless anyone can come up with a better idea (I do wonder about doing something horrible with pmu->dev.parent...) My bad for missing that rather subtle point the first time around, sorry everyone!
Robin.
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