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Subject[PATCH v2 7/7] arm64: capabilities: Batch cpu_enable callbacks
Date
We use a stop_machine call for each available capability to
enable it on all the CPUs available at boot time. Instead
we could batch the cpu_enable callbacks to a single stop_machine()
call to save us some time.

Reviewed-by: Vladimiri Murzin <vladimir.murzin@arm.com>
Tested-by: Vladimiri Murzin <vladimir.murzin@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
arch/arm64/include/asm/cpufeature.h | 3 ++
arch/arm64/kernel/cpufeature.c | 70 +++++++++++++++++++++++--------------
2 files changed, 47 insertions(+), 26 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 7e2ec64..0a15e2c 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -357,6 +357,9 @@ extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
extern struct static_key_false arm64_const_caps_ready;

+#define for_each_available_cap(cap) \
+ for_each_set_bit(cap, cpu_hwcaps, ARM64_NCAPS)
+
bool this_cpu_has_cap(unsigned int cap);

static inline bool cpu_have_feature(unsigned int num)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 13d729c..b12b9933 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1531,11 +1531,27 @@ static void update_cpu_capabilities(u16 scope_mask)
}
}

-static int __enable_cpu_capability(void *arg)
+/*
+ * Enable all the available capabilities on this CPU. The capabilities
+ * with BOOT_CPU scope are handled separately and hence skipped here.
+ */
+static int cpu_enable_non_boot_scope_capabilities(void *__unused)
{
- const struct arm64_cpu_capabilities *cap = arg;
+ int i;
+ u16 non_boot_scope = SCOPE_ALL & ~SCOPE_BOOT_CPU;

- cap->cpu_enable(cap);
+ for_each_available_cap(i) {
+ const struct arm64_cpu_capabilities *cap = cpu_hwcaps_ptrs[i];
+
+ if (WARN_ON(!cap))
+ continue;
+
+ if (!(cap->type & non_boot_scope))
+ continue;
+
+ if (cap->cpu_enable)
+ cap->cpu_enable(cap);
+ }
return 0;
}

@@ -1543,21 +1559,29 @@ static int __enable_cpu_capability(void *arg)
* Run through the enabled capabilities and enable() it on all active
* CPUs
*/
-static void __init
-__enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
- u16 scope_mask)
+static void __init enable_cpu_capabilities(u16 scope_mask)
{
+ int i;
+ const struct arm64_cpu_capabilities *caps;
+ bool boot_scope;
+
scope_mask &= ARM64_CPUCAP_SCOPE_MASK;
- for (; caps->matches; caps++) {
- unsigned int num = caps->capability;
+ boot_scope = !!(scope_mask & SCOPE_BOOT_CPU);

- if (!(caps->type & scope_mask) || !cpus_have_cap(num))
+ for (i = 0; i < ARM64_NCAPS; i++) {
+ unsigned int num;
+
+ caps = cpu_hwcaps_ptrs[i];
+ if (!caps || !(caps->type & scope_mask))
+ continue;
+ num = caps->capability;
+ if (!cpus_have_cap(num))
continue;

/* Ensure cpus_have_const_cap(num) works */
static_branch_enable(&cpu_hwcap_keys[num]);

- if (caps->cpu_enable) {
+ if (boot_scope && caps->cpu_enable)
/*
* Capabilities with SCOPE_BOOT_CPU scope are finalised
* before any secondary CPU boots. Thus, each secondary
@@ -1566,25 +1590,19 @@ __enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
* the boot CPU, for which the capability must be
* enabled here. This approach avoids costly
* stop_machine() calls for this case.
- *
- * Otherwise, use stop_machine() as it schedules the
- * work allowing us to modify PSTATE, instead of
- * on_each_cpu() which uses an IPI, giving us a PSTATE
- * that disappears when we return.
*/
- if (scope_mask & SCOPE_BOOT_CPU)
- caps->cpu_enable(caps);
- else
- stop_machine(__enable_cpu_capability,
- (void *)caps, cpu_online_mask);
- }
+ caps->cpu_enable(caps);
}
-}

-static void __init enable_cpu_capabilities(u16 scope_mask)
-{
- __enable_cpu_capabilities(arm64_errata, scope_mask);
- __enable_cpu_capabilities(arm64_features, scope_mask);
+ /*
+ * For all non-boot scope capabilities, use stop_machine()
+ * as it schedules the work allowing us to modify PSTATE,
+ * instead of on_each_cpu() which uses an IPI, giving us a
+ * PSTATE that disappears when we return.
+ */
+ if (!boot_scope)
+ stop_machine(cpu_enable_non_boot_scope_capabilities,
+ NULL, cpu_online_mask);
}

/*
--
2.7.4
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