linux-kernel - [PATCH v5 1/4] perf/x86/amd: ensure amd_pmu_core_disable

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Date: Mon,  1 Apr 2024 19:21:15 -0700
From: Andrii Nakryiko <andrii@...nel.org>
To: x86@...nel.org,
	peterz@...radead.org,
	mingo@...hat.com,
	tglx@...utronix.de
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	jolsa@...nel.org,
	song@...nel.org,
	kernel-team@...a.com,
	Andrii Nakryiko <andrii@...nel.org>,
	Sandipan Das <sandipan.das@....com>
Subject: [PATCH v5 1/4] perf/x86/amd: ensure amd_pmu_core_disable_all() is always inlined

In the following patches we will enable LBR capture on AMD CPUs at
arbitrary point in time, which means that LBR recording won't be frozen
by hardware automatically as part of hardware overflow event. So we need
to take care to minimize amount of branches and function calls/returns
on the path to freezing LBR, minimizing LBR snapshot altering as much as
possible.

amd_pmu_core_disable_all() is one of the functions on this path, and is
already marked as __always_inline. But it calls amd_pmu_set_global_ctl()
which is marked as just inline.  So to guarantee no function call will
be generated thoughout mark amd_pmu_set_global_ctl() as __always_inline
as well.

Reviewed-by: Sandipan Das <sandipan.das@....com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
---
 arch/x86/events/amd/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 985ef3b47919..9b15afda0326 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -647,7 +647,7 @@ static void amd_pmu_cpu_dead(int cpu)
 	}
 }

-static inline void amd_pmu_set_global_ctl(u64 ctl)
+static __always_inline void amd_pmu_set_global_ctl(u64 ctl)
 {
 	wrmsrl(MSR_AMD64_PERF_CNTR_GLOBAL_CTL, ctl);
 }
-- 
2.43.0