Re: [PATCH v5 06/13] powerpc/perf: IMC pmu cpumask and cpu hotplug support

From: Gautham R Shenoy
Date: Thu Mar 23 2017 - 07:52:57 EST

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In reply to: Madhavan Srinivasan: "[PATCH v5 06/13] powerpc/perf: IMC pmu cpumask and cpu hotplug support"
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Hi Hemant, Maddy,

On Thu, Mar 16, 2017 at 01:05:00PM +0530, Madhavan Srinivasan wrote:
> From: Hemant Kumar <hemant@xxxxxxxxxxxxxxxxxx>
>
> Adds cpumask attribute to be used by each IMC pmu. Only one cpu (any
> online CPU) from each chip for nest PMUs is designated to read counters.
>
> On CPU hotplug, dying CPU is checked to see whether it is one of the
> designated cpus, if yes, next online cpu from the same chip (for nest
> units) is designated as new cpu to read counters. For this purpose, we
> introduce a new state : CPUHP_AP_PERF_POWERPC_NEST_ONLINE.
>
> Cc: Gautham R. Shenoy <ego@xxxxxxxxxxxxxxxxxx>
> Cc: Balbir Singh <bsingharora@xxxxxxxxx>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Anton Blanchard <anton@xxxxxxxxx>
> Cc: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> Cc: Michael Neuling <mikey@xxxxxxxxxxx>
> Cc: Stewart Smith <stewart@xxxxxxxxxxxxxxxxxx>
> Cc: Daniel Axtens <dja@xxxxxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: Anju T Sudhakar <anju@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Hemant Kumar <hemant@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/opal-api.h | 3 +-
> arch/powerpc/include/asm/opal.h | 3 +
> arch/powerpc/perf/imc-pmu.c | 163 ++++++++++++++++++++++++-
> arch/powerpc/platforms/powernv/opal-wrappers.S | 1 +
> include/linux/cpuhotplug.h | 1 +
> 5 files changed, 169 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/opal-api.h b/arch/powerpc/include/asm/opal-api.h
> index a0aa285869b5..e1c3d4837857 100644
> --- a/arch/powerpc/include/asm/opal-api.h
> +++ b/arch/powerpc/include/asm/opal-api.h
> @@ -168,7 +168,8 @@
> #define OPAL_INT_SET_MFRR 125
> #define OPAL_PCI_TCE_KILL 126
> #define OPAL_NMMU_SET_PTCR 127
> -#define OPAL_LAST 127
> +#define OPAL_NEST_IMC_COUNTERS_CONTROL 145
> +#define OPAL_LAST 145
>
> /* Device tree flags */
>
> diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
> index 1ff03a6da76e..d93d08204243 100644
> --- a/arch/powerpc/include/asm/opal.h
> +++ b/arch/powerpc/include/asm/opal.h
> @@ -227,6 +227,9 @@ int64_t opal_pci_tce_kill(uint64_t phb_id, uint32_t kill_type,
> uint64_t dma_addr, uint32_t npages);
> int64_t opal_nmmu_set_ptcr(uint64_t chip_id, uint64_t ptcr);
>
> +int64_t opal_nest_imc_counters_control(uint64_t mode, uint64_t value1,
> + uint64_t value2, uint64_t value3);
> +
> /* Internal functions */
> extern int early_init_dt_scan_opal(unsigned long node, const char *uname,
> int depth, void *data);
> diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
> index f6f1ef9f56af..e46ff6d2a584 100644
> --- a/arch/powerpc/perf/imc-pmu.c
> +++ b/arch/powerpc/perf/imc-pmu.c
> @@ -16,6 +16,7 @@
> +static int ppc_nest_imc_cpu_online(unsigned int cpu)
> +{

I take it that 'cpu' is coming online.

> + int nid, fcpu, ncpu;
> + struct cpumask *l_cpumask, tmp_mask;
> +
> + /* Fint the cpumask of this node */
> + nid = cpu_to_node(cpu);
> + l_cpumask = cpumask_of_node(nid);
> +
> + /*
> + * If any of the cpu from this node is already present in the mask,
> + * just return, if not, then set this cpu in the mask.
> + */
> + if (!cpumask_and(&tmp_mask, l_cpumask, &nest_imc_cpumask)) {

In this case, none of the cpus in the node are in the mask. So we set
and this cpu in the imc cpumask and return.

> + cpumask_set_cpu(cpu, &nest_imc_cpumask);
> + return 0;
> + }

But this case implies that there is already a CPU from the node which
is in the imc_cpumask. As per the comment above, we are supposed to
just return. So why are we doing the following ?

Either the comment above is incorrect or I am missing something here.

> +
> + fcpu = cpumask_first(l_cpumask);
> + ncpu = cpumask_next(cpu, l_cpumask);
> + if (cpu == fcpu) {
> + if (cpumask_test_and_clear_cpu(ncpu, &nest_imc_cpumask)) {
> + cpumask_set_cpu(cpu, &nest_imc_cpumask);
> + nest_change_cpu_context(ncpu, cpu);
> + }
> + }

It seems that we want to set only the smallest online cpu in the node
in the nest_imc_cpumask. So, if the newly onlined cpu is the smallest,
we replace the previous representative with cpu.

So, the comment above needs to be fixed.

> +
> + return 0;
> +}
> +
> +static int ppc_nest_imc_cpu_offline(unsigned int cpu)
> +{
> + int nid, target = -1;
> + struct cpumask *l_cpumask;
> +
> + /*
> + * Check in the designated list for this cpu. Dont bother
> + * if not one of them.
> + */
> + if (!cpumask_test_and_clear_cpu(cpu, &nest_imc_cpumask))
> + return 0;
> +
> + /*
> + * Now that this cpu is one of the designated,
> + * find a next cpu a) which is online and b) in same chip.
> + */
> + nid = cpu_to_node(cpu);
> + l_cpumask = cpumask_of_node(nid);
> + target = cpumask_next(cpu, l_cpumask);
> +
> + /*
> + * Update the cpumask with the target cpu and
> + * migrate the context if needed
> + */
> + if (target >= 0 && target <= nr_cpu_ids) {
> + cpumask_set_cpu(target, &nest_imc_cpumask);
> + nest_change_cpu_context(cpu, target);
> + }
> + return 0;
> +}
> +
> +static int nest_pmu_cpumask_init(void)
> +{
> + const struct cpumask *l_cpumask;
> + int cpu, nid;
> + int *cpus_opal_rc;
> +
> + if (!cpumask_empty(&nest_imc_cpumask))
> + return 0;
> +

> + /*
> + * Nest PMUs are per-chip counters. So designate a cpu
> + * from each chip for counter collection.
> + */
> + for_each_online_node(nid) {
> + l_cpumask = cpumask_of_node(nid);
> +
> + /* designate first online cpu in this node */
> + cpu = cpumask_first(l_cpumask);
> + cpumask_set_cpu(cpu, &nest_imc_cpumask);
> + }
> +

What happens if a cpu in nest_imc_cpumask goes offline at this point ?

Is that possible ?

> + /*
> + * Memory for OPAL call return value.
> + */
> + cpus_opal_rc = kzalloc((sizeof(int) * nr_cpu_ids), GFP_KERNEL);
> + if (!cpus_opal_rc)
> + goto fail;
> +
> + /* Initialize Nest PMUs in each node using designated cpus */
> + on_each_cpu_mask(&nest_imc_cpumask, (smp_call_func_t)nest_init,
> + (void *)cpus_opal_rc, 1);
> +
> + /* Check return value array for any OPAL call failure */
> + for_each_cpu(cpu, &nest_imc_cpumask) {
> + if (cpus_opal_rc[cpu])
> + goto fail;
> + }
> +
> + cpuhp_setup_state(CPUHP_AP_PERF_POWERPC_NEST_ONLINE,
> + "POWER_NEST_IMC_ONLINE",
> + ppc_nest_imc_cpu_online,
> + ppc_nest_imc_cpu_offline);
> +
> + return 0;
> +
> +fail:
> + return -ENODEV;
> +}
> +
> static int nest_imc_event_init(struct perf_event *event)
> {
> int chip_id;
> @@ -63,7 +218,7 @@ static int nest_imc_event_init(struct perf_event *event)
> chip_id = topology_physical_package_id(event->cpu);
> pcni = &nest_perchip_info[chip_id];
> event->hw.event_base = pcni->vbase[config/PAGE_SIZE] +
> - (config & ~PAGE_MASK);
> + (config & ~PAGE_MASK);
>
> return 0;
> }
> @@ -122,6 +277,7 @@ static int update_pmu_ops(struct imc_pmu *pmu)
> pmu->pmu.stop = imc_event_stop;
> pmu->pmu.read = imc_perf_event_update;
> pmu->attr_groups[1] = &imc_format_group;
> + pmu->attr_groups[2] = &imc_pmu_cpumask_attr_group;
> pmu->pmu.attr_groups = pmu->attr_groups;
>
> return 0;
> @@ -189,6 +345,11 @@ int init_imc_pmu(struct imc_events *events, int idx,
> {
> int ret = -ENODEV;
>
> + /* Add cpumask and register for hotplug notification */
> + ret = nest_pmu_cpumask_init();
> + if (ret)
> + return ret;
> +
> ret = update_events_in_group(events, idx, pmu_ptr);
> if (ret)
> goto err_free;
> diff --git a/arch/powerpc/platforms/powernv/opal-wrappers.S b/arch/powerpc/platforms/powernv/opal-wrappers.S
> index da8a0f7a035c..b7208d8e6cc0 100644
> --- a/arch/powerpc/platforms/powernv/opal-wrappers.S
> +++ b/arch/powerpc/platforms/powernv/opal-wrappers.S
> @@ -301,3 +301,4 @@ OPAL_CALL(opal_int_eoi, OPAL_INT_EOI);
> OPAL_CALL(opal_int_set_mfrr, OPAL_INT_SET_MFRR);
> OPAL_CALL(opal_pci_tce_kill, OPAL_PCI_TCE_KILL);
> OPAL_CALL(opal_nmmu_set_ptcr, OPAL_NMMU_SET_PTCR);
> +OPAL_CALL(opal_nest_imc_counters_control, OPAL_NEST_IMC_COUNTERS_CONTROL);
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 62d240e962f0..cfb0cedc72af 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -136,6 +136,7 @@ enum cpuhp_state {
> CPUHP_AP_PERF_ARM_CCI_ONLINE,
> CPUHP_AP_PERF_ARM_CCN_ONLINE,
> CPUHP_AP_PERF_ARM_L2X0_ONLINE,
> + CPUHP_AP_PERF_POWERPC_NEST_ONLINE,
> CPUHP_AP_PERF_ARM_QCOM_L2_ONLINE,
> CPUHP_AP_WORKQUEUE_ONLINE,
> CPUHP_AP_RCUTREE_ONLINE,
> --
> 2.7.4
>

Next message: Arushi Singhal: "[PATCH] staging: tsl2x7x: Moved contents of the header to the source file."
Previous message: Lee Jones: "Re: [PATCH 05/13] platform/chrome: cros_ec_lpc: Add R/W helpers to LPC protocol variants"
In reply to: Madhavan Srinivasan: "[PATCH v5 06/13] powerpc/perf: IMC pmu cpumask and cpu hotplug support"
Next in thread: Madhavan Srinivasan: "[PATCH v5 05/13] powerpc/perf: Generic imc pmu event functions"
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