Re: [PATCH 1/4] drivers/perf: Add support for ARMv8.3-SPE

From: Suzuki K Poulose
Date: Fri Jul 31 2020 - 09:56:37 EST

On 07/31/2020 01:18 PM, liwei (GF) wrote:

On 2020/7/30 16:14, Leo Yan wrote:
Hi Suzuki,

On Wed, Jul 29, 2020 at 10:12:50AM +0100, Suzuki Kuruppassery Poulose wrote:
On 07/24/2020 10:16 AM, Wei Li wrote:
Armv8.3 extends the SPE by adding:
- Alignment field in the Events packet, and filtering on this event
using PMSEVFR_EL1.
- Support for the Scalable Vector Extension (SVE).

The main additions for SVE are:
- Recording the vector length for SVE operations in the Operation Type
packet. It is not possible to filter on vector length.
- Incomplete predicate and empty predicate fields in the Events packet,
and filtering on these events using PMSEVFR_EL1.

Update the check of pmsevfr for empty/partial predicated SVE and
alignment event in kernel driver.

Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
arch/arm64/include/asm/sysreg.h | 4 +++-
drivers/perf/arm_spe_pmu.c | 18 ++++++++++++++----
2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 463175f80341..be4c44ccdb56 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -281,7 +281,6 @@
#define SYS_PMSEVFR_EL1 sys_reg(3, 0, 9, 9, 5)
-#define SYS_PMSEVFR_EL1_RES0 0x0000ffff00ff0f55UL
#define SYS_PMSLATFR_EL1 sys_reg(3, 0, 9, 9, 6)
@@ -769,6 +768,9 @@
#define ID_AA64DFR0_PMUVER_8_5 0x6
#define ID_AA64DFR0_PMUVER_IMP_DEF 0xf
+#define ID_AA64DFR0_PMSVER_8_2 0x1
+#define ID_AA64DFR0_PMSVER_8_3 0x2
#define ID_DFR0_PERFMON_8_1 0x4
diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
index e51ddb6d63ed..5ec7ee0c8fa1 100644
--- a/drivers/perf/arm_spe_pmu.c
+++ b/drivers/perf/arm_spe_pmu.c
@@ -54,7 +54,7 @@ struct arm_spe_pmu {
struct hlist_node hotplug_node;
int irq; /* PPI */
+ int pmuver;
u16 min_period;
u16 counter_sz;
@@ -80,6 +80,15 @@ struct arm_spe_pmu {
/* Keep track of our dynamic hotplug state */
static enum cpuhp_state arm_spe_pmu_online;
+static u64 sys_pmsevfr_el1_mask[] = {
+ [ID_AA64DFR0_PMSVER_8_2] = GENMASK_ULL(63, 48) | GENMASK_ULL(31, 24) |
+ GENMASK_ULL(15, 12) | BIT_ULL(7) | BIT_ULL(5) | BIT_ULL(3) |
+ BIT_ULL(1),
+ [ID_AA64DFR0_PMSVER_8_3] = GENMASK_ULL(63, 48) | GENMASK_ULL(31, 24) |
+ GENMASK_ULL(18, 17) | GENMASK_ULL(15, 11) | BIT_ULL(7) |
+ BIT_ULL(5) | BIT_ULL(3) | BIT_ULL(1),
enum arm_spe_pmu_buf_fault_action {
@@ -670,7 +679,7 @@ static int arm_spe_pmu_event_init(struct perf_event *event)
!cpumask_test_cpu(event->cpu, &spe_pmu->supported_cpus))
return -ENOENT;
- if (arm_spe_event_to_pmsevfr(event) & SYS_PMSEVFR_EL1_RES0)
+ if (arm_spe_event_to_pmsevfr(event) & ~sys_pmsevfr_el1_mask[spe_pmu->pmuver])
if (attr->exclude_idle)
@@ -937,6 +946,7 @@ static void __arm_spe_pmu_dev_probe(void *info)
fld, smp_processor_id());
+ spe_pmu->pmuver = fld;

How do we deal with cases where we have big.LITTLE system with differing
SPE versions ?

Good point.

The first question we need to answer is: how to define SPE version?
From my understanding, if SPE uses the same sample specification and
the same packet format, then we should consider the SPE is the same
version cross CPUs. So even some CPUs are ARMv8.2 and other CPUs are
ARMv8.3 variants, we still should take the SPE as the same version.

And when read the SPE driver in the file drivers/perf/arm_spe_pmu.c and
I concluded that so far the SPE perf driver is to only support SPE-v1
with single instance, it cannot support a complex usage case like

CPU0-3: ARMv8.2 architecture with SPE
CPU4-7: ARMv8.3 architecture with SPE

For this case, if we take SPE as two different versions, let's say
SPE-8.2 and SPE-8.3, then should the SPE driver need to create multi
perf PMU events? For example, we should create a perf PMU event
'arm_spe_8.2' and another PMU event 'arm_spe_8.3'.

As we have supported SPE v2 (ARMv8.3-SPE) now, if we add the new
of_device_id: "arm,statistical-profiling-extension-v2" and the new
platform_device_id: "arm,spe-v2", we may really support two instance now.
Even two different versions of SPE pmus which work on different range of
cores with the same PPI. Their functional scopes are the same as the PPI partitions.

Another option is we always take this as SPE-v1 and only create single
PMU event, just keep what's we are doing with the perf event
'arm_spe_0', but the driver needs to dynamically detect SPE PMU version
number in the function arm_spe_pmu_event_init(), and then based on
version number to select corresponding mask for PMSEVFR.

Thus, the driver will service two devices, and will also register two PMUs 'arm_spe_0' and
'arm_spe_1', so i think there is no conflict here.

Or the other option is to strictly support only one version - the lowest
version supported by the system, which is compatible with all the
others. This could be achieved by using the sanitised feature value of
the SPE version.


What do you prefer ?

Back to Suzuki's question, refer to the ACPI parsing code for SPE device, function
arm_spe_acpi_register_device(), there is a check of hetero_id for all cores.
It seems that we only support homogeneous ACPI/SPE machines, but i can't find the similar
check in OF/SPE parsing code.

I think the driver assumes that the system supports uniform version
of the SPE (which was valid when the driver was written).