[PATCH v4 0/3] Assorted fixes in RISC-V PMU driver

[PATCH v4 0/3] Assorted fixes in RISC-V PMU driver

[Atish Patra]

This series contains 3 fixes out of which the first one is a new fix
for invalid event data reported in lkml[2]. The last two are v3 of Samuel's
patch[1]. I added the RB/TB/Fixes tag and moved 1 unrelated change
to its own patch. I also changed an error message in kvm vcpu_pmu from
pr_err to pr_debug to avoid redundant failure error messages generated
due to the boot time quering of events implemented in the patch[1]

Here is the original cover letter for the patch[1]

Before this patch:
$ perf list hw

List of pre-defined events (to be used in -e or -M):

  branch-instructions OR branches                    [Hardware event]
  branch-misses                                      [Hardware event]
  bus-cycles                                         [Hardware event]
  cache-misses                                       [Hardware event]
  cache-references                                   [Hardware event]
  cpu-cycles OR cycles                               [Hardware event]
  instructions                                       [Hardware event]
  ref-cycles                                         [Hardware event]
  stalled-cycles-backend OR idle-cycles-backend      [Hardware event]
  stalled-cycles-frontend OR idle-cycles-frontend    [Hardware event]

$ perf stat -ddd true

 Performance counter stats for 'true':

              4.36 msec task-clock                       #    0.744 CPUs utilized
                 1      context-switches                 #  229.325 /sec
                 0      cpu-migrations                   #    0.000 /sec
                38      page-faults                      #    8.714 K/sec
         4,375,694      cycles                           #    1.003 GHz                         (60.64%)
           728,945      instructions                     #    0.17  insn per cycle
            79,199      branches                         #   18.162 M/sec
            17,709      branch-misses                    #   22.36% of all branches
           181,734      L1-dcache-loads                  #   41.676 M/sec
             5,547      L1-dcache-load-misses            #    3.05% of all L1-dcache accesses
     <not counted>      LLC-loads                                                               (0.00%)
     <not counted>      LLC-load-misses                                                         (0.00%)
     <not counted>      L1-icache-loads                                                         (0.00%)
     <not counted>      L1-icache-load-misses                                                   (0.00%)
     <not counted>      dTLB-loads                                                              (0.00%)
     <not counted>      dTLB-load-misses                                                        (0.00%)
     <not counted>      iTLB-loads                                                              (0.00%)
     <not counted>      iTLB-load-misses                                                        (0.00%)
     <not counted>      L1-dcache-prefetches                                                    (0.00%)
     <not counted>      L1-dcache-prefetch-misses                                               (0.00%)

       0.005860375 seconds time elapsed

       0.000000000 seconds user
       0.010383000 seconds sys

After this patch:
$ perf list hw

List of pre-defined events (to be used in -e or -M):

  branch-instructions OR branches                    [Hardware event]
  branch-misses                                      [Hardware event]
  cache-misses                                       [Hardware event]
  cache-references                                   [Hardware event]
  cpu-cycles OR cycles                               [Hardware event]
  instructions                                       [Hardware event]

$ perf stat -ddd true

 Performance counter stats for 'true':

              5.16 msec task-clock                       #    0.848 CPUs utilized
                 1      context-switches                 #  193.817 /sec
                 0      cpu-migrations                   #    0.000 /sec
                37      page-faults                      #    7.171 K/sec
         5,183,625      cycles                           #    1.005 GHz
           961,696      instructions                     #    0.19  insn per cycle
            85,853      branches                         #   16.640 M/sec
            20,462      branch-misses                    #   23.83% of all branches
           243,545      L1-dcache-loads                  #   47.203 M/sec
             5,974      L1-dcache-load-misses            #    2.45% of all L1-dcache accesses
   <not supported>      LLC-loads
   <not supported>      LLC-load-misses
   <not supported>      L1-icache-loads
   <not supported>      L1-icache-load-misses
   <not supported>      dTLB-loads
            19,619      dTLB-load-misses
   <not supported>      iTLB-loads
             6,831      iTLB-load-misses
   <not supported>      L1-dcache-prefetches
   <not supported>      L1-dcache-prefetch-misses

       0.006085625 seconds time elapsed

       0.000000000 seconds user
       0.013022000 seconds sys

Changes in v4:

- Added SoB tags.
- Improved the commit message in patch 1
- Link to v3: https://lore.kernel.org/r/20240626-misc_perf_fixes-v3-0-de3f8ed88dab@rivosinc.com

Changes in v3:
 - Added one more fix
 - Separated an unrelated change to its own patch.
 - Rebase and Added RB/TB/Fixes tag.
 - Changed a error message in kvm code to avoid unnecessary failures
   at guest booting.
Changes in v2:
 - Move the event checking to a workqueue to make it asynchronous
 - Add more details to the commit message based on the v1 discussion

[1] https://lore.kernel.org/linux-riscv/20240418014652.1143466-1-samuel.holland@sifive.com/
[2] https://lore.kernel.org/all/CC51D53B-846C-4D81-86FC-FBF969D0A0D6@pku.edu.cn/

Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
Atish Patra (1):
      drivers/perf: riscv: Do not update the event data if uptodate

Samuel Holland (2):
      drivers/perf: riscv: Reset the counter to hpmevent mapping while starting cpus
      perf: RISC-V: Check standard event availability

 arch/riscv/kvm/vcpu_pmu.c    |  2 +-
 drivers/perf/riscv_pmu.c     |  2 +-
 drivers/perf/riscv_pmu_sbi.c | 44 +++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 43 insertions(+), 5 deletions(-)
---
base-commit: 55027e689933ba2e64f3d245fb1ff185b3e7fc81
change-id: 20240625-misc_perf_fixes-5c57f555d828
--
Regards,
Atish patra

[PATCH v4 1/3] drivers/perf: riscv: Do not update the event data if uptodate

[Atish Patra]

In case of an counter overflow, the event data may get corrupted
if called from an external overflow handler. This happens because
we can't update the counter without starting it when SBI PMU
extension is in use. However, the prev_count has been already
updated at the first pass while the counter value is still the
old one.

The solution is simple where we don't need to update it again
if it is already updated which can be detected using hwc state.
The event state in the overflow handler is updated in the following
patch. Thus, this fix can't be backported to kernel version where
overflow support was added.

Fixes: a8625217a054 ("drivers/perf: riscv: Implement SBI PMU snapshot function")

Reported-by: garthlei@pku.edu.cn
Closes:https://lore.kernel.org/all/CC51D53B-846C-4D81-86FC-FBF969D0A0D6@pku.edu.cn/
Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 drivers/perf/riscv_pmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
index 78c490e0505a..0a02e85a8951 100644
--- a/drivers/perf/riscv_pmu.c
+++ b/drivers/perf/riscv_pmu.c
@@ -167,7 +167,7 @@ u64 riscv_pmu_event_update(struct perf_event *event)
 	unsigned long cmask;
 	u64 oldval, delta;
 
-	if (!rvpmu->ctr_read)
+	if (!rvpmu->ctr_read || (hwc->state & PERF_HES_UPTODATE))
 		return 0;
 
 	cmask = riscv_pmu_ctr_get_width_mask(event);

-- 
2.34.1

[PATCH v4 2/3] drivers/perf: riscv: Reset the counter to hpmevent mapping while starting cpus

[Atish Patra]

From: Samuel Holland <samuel.holland@sifive.com>

Currently, we stop all the counters while a new cpu is brought online.
However, the hpmevent to counter mappings are not reset. The firmware may
have some stale encoding in their mapping structure which may lead to
undesirable results. We have not encountered such scenario though.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 drivers/perf/riscv_pmu_sbi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index a2e4005e1fd0..94bc369a3454 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c
@@ -762,7 +762,7 @@ static inline void pmu_sbi_stop_all(struct riscv_pmu *pmu)
 	 * which may include counters that are not enabled yet.
 	 */
 	sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP,
-		  0, pmu->cmask, 0, 0, 0, 0);
+		  0, pmu->cmask, SBI_PMU_STOP_FLAG_RESET, 0, 0, 0);
 }
 
 static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)

-- 
2.34.1

[PATCH v4 3/3] perf: RISC-V: Check standard event availability

[Atish Patra]

From: Samuel Holland <samuel.holland@sifive.com>

The RISC-V SBI PMU specification defines several standard hardware and
cache events. Currently, all of these events are exposed to userspace,
even when not actually implemented. They appear in the `perf list`
output, and commands like `perf stat` try to use them.

This is more than just a cosmetic issue, because the PMU driver's .add
function fails for these events, which causes pmu_groups_sched_in() to
prematurely stop scheduling in other (possibly valid) hardware events.

Add logic to check which events are supported by the hardware (i.e. can
be mapped to some counter), so only usable events are reported to
userspace. Since the kernel does not know the mapping between events and
possible counters, this check must happen during boot, when no counters
are in use. Make the check asynchronous to minimize impact on boot time.

Fixes: e9991434596f ("RISC-V: Add perf platform driver based on SBI PMU extension")

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 arch/riscv/kvm/vcpu_pmu.c    |  2 +-
 drivers/perf/riscv_pmu_sbi.c | 42 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
index 04db1f993c47..bcf41d6e0df0 100644
--- a/arch/riscv/kvm/vcpu_pmu.c
+++ b/arch/riscv/kvm/vcpu_pmu.c
@@ -327,7 +327,7 @@ static long kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_att
 
 	event = perf_event_create_kernel_counter(attr, -1, current, kvm_riscv_pmu_overflow, pmc);
 	if (IS_ERR(event)) {
-		pr_err("kvm pmu event creation failed for eidx %lx: %ld\n", eidx, PTR_ERR(event));
+		pr_debug("kvm pmu event creation failed for eidx %lx: %ld\n", eidx, PTR_ERR(event));
 		return PTR_ERR(event);
 	}
 
diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index 94bc369a3454..4e842dcedfba 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c
@@ -20,6 +20,7 @@
 #include <linux/cpu_pm.h>
 #include <linux/sched/clock.h>
 #include <linux/soc/andes/irq.h>
+#include <linux/workqueue.h>
 
 #include <asm/errata_list.h>
 #include <asm/sbi.h>
@@ -114,7 +115,7 @@ struct sbi_pmu_event_data {
 	};
 };
 
-static const struct sbi_pmu_event_data pmu_hw_event_map[] = {
+static struct sbi_pmu_event_data pmu_hw_event_map[] = {
 	[PERF_COUNT_HW_CPU_CYCLES]		= {.hw_gen_event = {
 							SBI_PMU_HW_CPU_CYCLES,
 							SBI_PMU_EVENT_TYPE_HW, 0}},
@@ -148,7 +149,7 @@ static const struct sbi_pmu_event_data pmu_hw_event_map[] = {
 };
 
 #define C(x) PERF_COUNT_HW_CACHE_##x
-static const struct sbi_pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_MAX]
+static struct sbi_pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_MAX]
 [PERF_COUNT_HW_CACHE_OP_MAX]
 [PERF_COUNT_HW_CACHE_RESULT_MAX] = {
 	[C(L1D)] = {
@@ -293,6 +294,34 @@ static const struct sbi_pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_M
 	},
 };
 
+static void pmu_sbi_check_event(struct sbi_pmu_event_data *edata)
+{
+	struct sbiret ret;
+
+	ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_CFG_MATCH,
+			0, cmask, 0, edata->event_idx, 0, 0);
+	if (!ret.error) {
+		sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP,
+			  ret.value, 0x1, SBI_PMU_STOP_FLAG_RESET, 0, 0, 0);
+	} else if (ret.error == SBI_ERR_NOT_SUPPORTED) {
+		/* This event cannot be monitored by any counter */
+		edata->event_idx = -EINVAL;
+	}
+}
+
+static void pmu_sbi_check_std_events(struct work_struct *work)
+{
+	for (int i = 0; i < ARRAY_SIZE(pmu_hw_event_map); i++)
+		pmu_sbi_check_event(&pmu_hw_event_map[i]);
+
+	for (int i = 0; i < ARRAY_SIZE(pmu_cache_event_map); i++)
+		for (int j = 0; j < ARRAY_SIZE(pmu_cache_event_map[i]); j++)
+			for (int k = 0; k < ARRAY_SIZE(pmu_cache_event_map[i][j]); k++)
+				pmu_sbi_check_event(&pmu_cache_event_map[i][j][k]);
+}
+
+static DECLARE_WORK(check_std_events_work, pmu_sbi_check_std_events);
+
 static int pmu_sbi_ctr_get_width(int idx)
 {
 	return pmu_ctr_list[idx].width;
@@ -478,6 +507,12 @@ static int pmu_sbi_event_map(struct perf_event *event, u64 *econfig)
 	u64 raw_config_val;
 	int ret;
 
+	/*
+	 * Ensure we are finished checking standard hardware events for
+	 * validity before allowing userspace to configure any events.
+	 */
+	flush_work(&check_std_events_work);
+
 	switch (type) {
 	case PERF_TYPE_HARDWARE:
 		if (config >= PERF_COUNT_HW_MAX)
@@ -1359,6 +1394,9 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 	if (ret)
 		goto out_unregister;
 
+	/* Asynchronously check which standard events are available */
+	schedule_work(&check_std_events_work);
+
 	return 0;
 
 out_unregister:

-- 
2.34.1

Re: [PATCH v4 0/3] Assorted fixes in RISC-V PMU driver

[Will Deacon]

On Fri, Jun 28, 2024 at 12:51:40AM -0700, Atish Patra wrote:
> This series contains 3 fixes out of which the first one is a new fix
> for invalid event data reported in lkml[2]. The last two are v3 of Samuel's
> patch[1]. I added the RB/TB/Fixes tag and moved 1 unrelated change
> to its own patch. I also changed an error message in kvm vcpu_pmu from
> pr_err to pr_debug to avoid redundant failure error messages generated
> due to the boot time quering of events implemented in the patch[1]

I'm assuming this series will go via the riscv arch tree, but please
shout if that's not the case.

Will

Re: [PATCH v4 0/3] Assorted fixes in RISC-V PMU driver

[Palmer Dabbelt]

On Mon, 01 Jul 2024 06:01:27 PDT (-0700), Will Deacon wrote:
> On Fri, Jun 28, 2024 at 12:51:40AM -0700, Atish Patra wrote:
>> This series contains 3 fixes out of which the first one is a new fix
>> for invalid event data reported in lkml[2]. The last two are v3 of Samuel's
>> patch[1]. I added the RB/TB/Fixes tag and moved 1 unrelated change
>> to its own patch. I also changed an error message in kvm vcpu_pmu from
>> pr_err to pr_debug to avoid redundant failure error messages generated
>> due to the boot time quering of events implemented in the patch[1]
>
> I'm assuming this series will go via the riscv arch tree, but please
> shout if that's not the case.

Ya, it just ended up dragging on a bit because of a missing DCO.  I'm 
just throwing it at the tester now, it should show up on fixes 
eventually...

Re: [PATCH v4 0/3] Assorted fixes in RISC-V PMU driver

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Fri, 28 Jun 2024 00:51:40 -0700 you wrote:
> This series contains 3 fixes out of which the first one is a new fix
> for invalid event data reported in lkml[2]. The last two are v3 of Samuel's
> patch[1]. I added the RB/TB/Fixes tag and moved 1 unrelated change
> to its own patch. I also changed an error message in kvm vcpu_pmu from
> pr_err to pr_debug to avoid redundant failure error messages generated
> due to the boot time quering of events implemented in the patch[1]
> 
> [...]

Here is the summary with links:
  - [v4,1/3] drivers/perf: riscv: Do not update the event data if uptodate
    https://git.kernel.org/riscv/c/a3f24e83d11d
  - [v4,2/3] drivers/perf: riscv: Reset the counter to hpmevent mapping while starting cpus
    https://git.kernel.org/riscv/c/7dd646cf745c
  - [v4,3/3] perf: RISC-V: Check standard event availability
    https://git.kernel.org/riscv/c/16d3b1af0944

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html