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Date: Wed, 19 Jun 2024 17:20:46 -0700
From: Atish Patra <atishp@...shpatra.org>
To: Alexandre Ghiti <alex@...ti.fr>, Samuel Holland <samuel.holland@...ive.com>
Cc: Atish Patra <atishp@...osinc.com>, Anup Patel <anup@...infault.org>,
Albert Ou <aou@...s.berkeley.edu>, Mark Rutland <mark.rutland@....com>,
Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>,
Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2] perf: RISC-V: Check standard event availability
On Tue, Jun 18, 2024 at 12:48 AM Alexandre Ghiti <alex@...ti.fr> wrote:
>
> Hi Samuel, Atish,
>
> On 24/05/2024 22:00, Alexandre Ghiti wrote:
> > Hi Samuel,
> >
> > On 26/04/2024 17:38, Atish Patra wrote:
> >> On 4/17/24 18:46, Samuel Holland wrote:
> >>> 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.
> >>>
> >>> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> >>> ---
> >>> 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 v2:
> >>> - Move the event checking to a workqueue to make it asynchronous
> >>> - Add more details to the commit message based on the v1 discussion
> >>>
> >>> drivers/perf/riscv_pmu_sbi.c | 45
> >>> +++++++++++++++++++++++++++++++++---
> >>> 1 file changed, 42 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/drivers/perf/riscv_pmu_sbi.c
> >>> b/drivers/perf/riscv_pmu_sbi.c
> >>> index 8cbe6e5f9c39..c326954af066 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>
> >>> @@ -109,7 +110,7 @@ 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}},
> >>> @@ -143,7 +144,7 @@ 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)] = {
> >>> @@ -288,6 +289,34 @@ 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;
> >>> @@ -473,6 +502,12 @@ 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)
> >>> @@ -634,7 +669,8 @@ 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);
> >>> +
> >>
> >> Why is this required for this patch?
> >>
> >> If the intention is a generic improvement to reset mhpmevent at boot
> >> time, it should be separate patch.
> >>
> >>> }
> >>> static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)
> >>> @@ -1108,6 +1144,9 @@ static int pmu_sbi_device_probe(struct
> >>> platform_device *pdev)
> >>> register_sysctl("kernel", sbi_pmu_sysctl_table);
> >>> + /* Asynchronously check which standard events are available */
> >>> + schedule_work(&check_std_events_work);
> >>> +
> >>> return 0;
> >>> out_unregister:
> >>
> >> Until we have the new SBI interface defined to optimize these SBI
> >> calls, we can use this individual call approach to fix the current
> >> issue.
> >>
> >> lgtm otherwise.
> >>
> >> Reviewed-by: Atish Patra <atishp@...osinc.com>
> >> Tested-by: Atish Patra <atishp@...osinc.com>
> >
> >
> > Can you add a Fixes tag for this so that we can merge in 6.10-rcX?
> >
> > Thanks,
> >
> > Alex
>
>
> So I'd choose the following commit as a Fixes tag: e9991434596f
> ("RISC-V: Add perf platform driver based on SBI PMU extension")
>
> In addition, this patch does not apply cleanly on top of 6.10, the
> resolution I came up with is there
> https://github.com/linux-riscv/linux-riscv/pull/1043/commits/0a440d8b9e90117261f02f4d019359847c64cb38
>
> Can you guys check it's correct?
>
Looks okay to me. I will test it once again with the latest upstream.
As per my previous comment, I am still not sure if we need the
STOP_FLAG_RESET update in stop_all in this patch context[1].
@Samuel Holland : Let me know If you are busy with other things. I can
split the patch and send v3 if required.
[1] https://lore.kernel.org/linux-arm-kernel/79087773-9115-4d4c-b566-028a21049d61@rivosinc.com/T/#m75e4f6562338a0515464ebf60d35915f60edb71e
> Thanks,
>
> Alex
>
>
> >
> >
> >>
> >>
> >> _______________________________________________
> >> linux-riscv mailing list
> >> linux-riscv@...ts.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-riscv
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
--
Regards,
Atish
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