Subject: Re: [PATCH V12 05/10] arm64/perf: Add branch stack support in ARMV8 PMU

From: Marc Zyngier <[email-masked]>
Date: Mon, 19 Jun 2023 10:08:07 +0100

On Mon, 19 Jun 2023 06:45:07 +0100,
Anshuman Khandual <[email-masked]> wrote:
> 
> 
> 
> On 6/16/23 14:51, Catalin Marinas wrote:
> > On Fri, Jun 16, 2023 at 06:57:52AM +0530, Anshuman Khandual wrote:
> >> On 6/16/23 05:12, kernel test robot wrote:
> >>> kernel test robot noticed the following build errors:
> >>>
> >>> [auto build test ERROR on arm64/for-next/core]
> >>> [also build test ERROR on tip/perf/core acme/perf/core linus/master v6.4-rc6 next-20230615]
> >>> [If your patch is applied to the wrong git tree, kindly drop us a note.
> >>> And when submitting patch, we suggest to use '--base' as documented in
> >>> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> >>>
> >>> url:    https://github.com/intel-lab-lkp/linux/commits/Anshuman-Khandual/drivers-perf-arm_pmu-Add-new-sched_task-callback/20230615-223352
> >>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
> >>> patch link:    https://lore.kernel.org/r/20230615133239.442736-6-anshuman.khandual%40arm.com
> >>> patch subject: [PATCH V12 05/10] arm64/perf: Add branch stack support in ARMV8 PMU
> >>> config: arm-randconfig-r004-20230615 (https://download.01.org/0day-ci/archive/20230616/[email-masked]/config)
> >>> compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
> >>> reproduce (this is a W=1 build):
> >>>         mkdir -p ~/bin
> >>>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >>>         chmod +x ~/bin/make.cross
> >>>         # install arm cross compiling tool for clang build
> >>>         # apt-get install binutils-arm-linux-gnueabi
> >>>         git remote add arm64 https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
> >>>         git fetch arm64 for-next/core
> >>>         git checkout arm64/for-next/core
> >>>         b4 shazam https://lore.kernel.org/r/[email-masked]
> >>>         # save the config file
> >>>         mkdir build_dir && cp config build_dir/.config
> >>>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=arm olddefconfig
> >>>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash drivers/perf/
> >>
> >> I am unable to reproduce this on mainline 6.4-rc6 via default cross compiler
> >> on a W=1 build. Looking at all other problems reported on the file, it seems
> >> something is not right here. Reported build problems around these callbacks,
> >> i.e armv8pmu_branch_XXXX() do not make sense as they are available via config
> >> CONFIG_PERF_EVENTS which is also enabled along with CONFIG_ARM_PMUV3 in this
> >> test config.
> > 
> > Have you tried applying this series on top of the arm64 for-next/core
> > branch? That's what the robot it testing (in the absence of a --base
> > option when generating the patches).
> 
> Right, it turned out to be a build problem on arm (32 bit) platform instead.
> After arm_pmuv3.c moved into common ./drivers/perf from ./arch/arm64/kernel/,
> it can no longer access arch/arm64/include/asm/perf_event.h defined functions
> without breaking arm (32) bit. The following code block needs to be moved out
> from arch/arm64/include/asm/perf_event.h into include/linux/perf/arm_pmuv3.h
> (which is preferred as all call sites are inside drivers/perf/arm_pmuv3.c) or
> may be arm_pmu.h (which is one step higher in the abstraction).

No, that's the wrong approach. The 32bit backend must have its own
stubs for the stuff it implements or not.

Just add something like the patch below, and please *test* that a
32bit VM using PMUv3 doesn't have any regression.

Thanks,

	M.

>From 017362ca518e6d6ac3262514d1f7f27e73232799 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <[email-masked]>
Date: Mon, 19 Jun 2023 10:05:52 +0100
Subject: [PATCH] 32bit hack

Signed-off-by: Marc Zyngier <[email-masked]>
---
 arch/arm/include/asm/arm_pmuv3.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/arm/include/asm/arm_pmuv3.h b/arch/arm/include/asm/arm_pmuv3.h
index f4db3e75d75f..c4bcb7a18267 100644
--- a/arch/arm/include/asm/arm_pmuv3.h
+++ b/arch/arm/include/asm/arm_pmuv3.h
@@ -244,4 +244,22 @@ static inline bool is_pmuv3p5(int pmuver)
 	return pmuver >= ARMV8_PMU_DFR_VER_V3P5;
 }
 
+/* BRBE stubs */
+static inline void armv8pmu_branch_enable(struct perf_event *event) { }
+static inline void armv8pmu_branch_disable(struct perf_event *event) { }
+static inline void armv8pmu_branch_read(struct pmu_hw_events * cpuc,
+					struct perf_event *event) { }
+static inline void armv8pmu_branch_save(struct arm_pmu *armpmu, void *ctx) {}
+static inline void armv8pmu_branch_reset(void) {}
+static inline bool armv8pmu_branch_attr_valid(struct perf_event *event)
+{
+	return false;
+}
+static inline void armv8pmu_branch_probe(struct arm_pmu *armpmu) {}
+static inline int armv8pmu_task_ctx_cache_alloc(struct arm_pmu *armpmu)
+{
+	return 0;
+}
+static inline void armv8pmu_task_ctx_cache_free(struct arm_pmu *armpmu) {}
+
 #endif
-- 
2.39.2

-- 
Without deviation from the norm, progress is not possible.

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