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Date: Tue, 11 Sep 2018 16:17:50 +0100
From: Mark Rutland <mark.rutland@....com>
To: Hoan Tran <hoan.tran@...erecomputing.com>
Cc: Will Deacon <will.deacon@....com>, loc.ho@...erecomputing.com,
khuong.dinh@...erecomputing.com,
Tai Nguyen <ttnguyen@...erecomputing.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: xgene: Add CPU hotplug support
On Wed, Aug 15, 2018 at 11:31:35AM -0700, Hoan Tran wrote:
> This patch adds CPU hotplug support where the PMU migrates the context to
> another online CPU when its CPU is offline.
>
> It fixes the below issue where the user does offline the CPU which is assigned
> to this PMU.
>
> Assuming, CPU0 is assigned for this PMU. When the user does offline CPU0
> [root@(none) ~]# echo 0 > /sys/devices/system/cpu/cpu0/online
> This PMU does not work anymore and shows the below error.
> [root@(none) ~]# perf stat -a -e l3c0/cycle-count/,l3c0/write/ sleep 1
> Error:
> The sys_perf_event_open() syscall returned with 19 (No such device) for event (l3c0/cycle-count/).
> /bin/dmesg may provide additional information.
> No CONFIG_PERF_EVENTS=y kernel support configured?
>
> With this patch, when CPU0 is offline, PMU migrates to another online CPU and
> works on that CPU.
>
> Signed-off-by: Hoan Tran <hoan.tran@...erecomputing.com>
> ---
> drivers/perf/xgene_pmu.c | 71 ++++++++++++++++++++++++++++++++++++++++++----
> include/linux/cpuhotplug.h | 1 +
> 2 files changed, 66 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/perf/xgene_pmu.c b/drivers/perf/xgene_pmu.c
> index 0e31f13..248a3f7 100644
> --- a/drivers/perf/xgene_pmu.c
> +++ b/drivers/perf/xgene_pmu.c
> @@ -21,6 +21,7 @@
>
> #include <linux/acpi.h>
> #include <linux/clk.h>
> +#include <linux/cpuhotplug.h>
> #include <linux/cpumask.h>
> #include <linux/interrupt.h>
> #include <linux/io.h>
> @@ -130,12 +131,14 @@ struct xgene_pmu_ops {
>
> struct xgene_pmu {
> struct device *dev;
> + struct hlist_node node;
> int version;
> void __iomem *pcppmu_csr;
> u32 mcb_active_mask;
> u32 mc_active_mask;
> u32 l3c_active_mask;
> cpumask_t cpu;
> + int irq;
> raw_spinlock_t lock;
> const struct xgene_pmu_ops *ops;
> struct list_head l3cpmus;
> @@ -1806,6 +1809,53 @@ static const struct acpi_device_id xgene_pmu_acpi_match[] = {
> MODULE_DEVICE_TABLE(acpi, xgene_pmu_acpi_match);
> #endif
>
> +static int xgene_pmu_online_cpu(unsigned int cpu, struct hlist_node *node)
> +{
> + struct xgene_pmu *xgene_pmu = hlist_entry_safe(node, struct xgene_pmu,
> + node);
> +
> + if (cpumask_empty(&xgene_pmu->cpu))
> + cpumask_set_cpu(cpu, &xgene_pmu->cpu);
> +
> + /* Overflow interrupt also should use the same CPU */
> + WARN_ON(irq_set_affinity(xgene_pmu->irq, &xgene_pmu->cpu));
> +
> + return 0;
> +}
> +
> +static int xgene_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
> +{
> + struct xgene_pmu *xgene_pmu = hlist_entry_safe(node, struct xgene_pmu,
> + node);
> + struct xgene_pmu_dev_ctx *ctx;
> + unsigned int target;
> +
> + if (!cpumask_test_and_clear_cpu(cpu, &xgene_pmu->cpu))
> + return 0;
> + target = cpumask_any_but(cpu_online_mask, cpu);
> + if (target >= nr_cpu_ids)
> + return 0;
> +
> + list_for_each_entry(ctx, &xgene_pmu->mcpmus, next) {
> + perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
> + }
> + list_for_each_entry(ctx, &xgene_pmu->mcbpmus, next) {
> + perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
> + }
> + list_for_each_entry(ctx, &xgene_pmu->l3cpmus, next) {
> + perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
> + }
> + list_for_each_entry(ctx, &xgene_pmu->iobpmus, next) {
> + perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
> + }
> +
> + cpumask_set_cpu(target, &xgene_pmu->cpu);
> + /* Overflow interrupt also should use the same CPU */
> + WARN_ON(irq_set_affinity(xgene_pmu->irq, &xgene_pmu->cpu));
> +
> + return 0;
> +}
> +
> static int xgene_pmu_probe(struct platform_device *pdev)
> {
> const struct xgene_pmu_data *dev_data;
> @@ -1815,6 +1865,14 @@ static int xgene_pmu_probe(struct platform_device *pdev)
> int irq, rc;
> int version;
>
> + /* Install a hook to update the reader CPU in case it goes offline */
> + rc = cpuhp_setup_state_multi(CPUHP_AP_PERF_XGENE_ONLINE,
> + "CPUHP_AP_PERF_XGENE_ONLINE",
> + xgene_pmu_online_cpu,
> + xgene_pmu_offline_cpu);
> + if (rc)
> + return rc;
> +
> xgene_pmu = devm_kzalloc(&pdev->dev, sizeof(*xgene_pmu), GFP_KERNEL);
> if (!xgene_pmu)
> return -ENOMEM;
> @@ -1865,6 +1923,7 @@ static int xgene_pmu_probe(struct platform_device *pdev)
> dev_err(&pdev->dev, "No IRQ resource\n");
> return -EINVAL;
> }
> +
> rc = devm_request_irq(&pdev->dev, irq, xgene_pmu_isr,
> IRQF_NOBALANCING | IRQF_NO_THREAD,
> dev_name(&pdev->dev), xgene_pmu);
> @@ -1873,6 +1932,8 @@ static int xgene_pmu_probe(struct platform_device *pdev)
> return rc;
> }
>
> + xgene_pmu->irq = irq;
> +
> raw_spin_lock_init(&xgene_pmu->lock);
>
> /* Check for active MCBs and MCUs */
> @@ -1883,13 +1944,11 @@ static int xgene_pmu_probe(struct platform_device *pdev)
> xgene_pmu->mc_active_mask = 0x1;
> }
>
> - /* Pick one core to use for cpumask attributes */
> - cpumask_set_cpu(smp_processor_id(), &xgene_pmu->cpu);
> -
> - /* Make sure that the overflow interrupt is handled by this CPU */
> - rc = irq_set_affinity(irq, &xgene_pmu->cpu);
> + /* Add this instance to the list used by the hotplug callback */
> + rc = cpuhp_state_add_instance(CPUHP_AP_PERF_XGENE_ONLINE,
> + &xgene_pmu->node);
> if (rc) {
> - dev_err(&pdev->dev, "Failed to set interrupt affinity!\n");
> + dev_err(&pdev->dev, "Error %d registering hotplug", rc);
> return rc;
> }
You also need to remove the cpuhp instances when unregistering the PMUs
in xgene_pmu_dev_cleanup().
Otherwise this looks fine to me, on the assumption the system PMU is
accessible from all CPUs in the system (e.g. it's not lcoal to a socket
or anything like that).
Thanks,
Mark.
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