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SubjectRe: [PATCH 3/3] perf/x86/intel: force resched when TFA sysctl is modified
On Thu, Apr 04, 2019 at 11:32:19AM -0700, Stephane Eranian wrote:
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index a4b7711ef0ee..8d356c2096bc 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -4483,6 +4483,60 @@ static ssize_t freeze_on_smi_store(struct device *cdev,
> return count;
> }
>
> +static void update_tfa_sched(void *ignored)
> +{
> + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> + struct pmu *pmu = x86_get_pmu();
> + struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
> + struct perf_event_context *task_ctx = cpuctx->task_ctx;
> +
> + /* prevent any changes to the two contexts */
> + perf_ctx_lock(cpuctx, task_ctx);
> +
> + /*
> + * check if PMC3 is used
> + * and if so force schedule out for all event types all contexts
> + */
> + if (test_bit(3, cpuc->active_mask))
> + perf_ctx_resched(cpuctx, task_ctx, EVENT_ALL|EVENT_CPU);
> +
> + perf_ctx_unlock(cpuctx, task_ctx);

I'm not particularly happy with exporting all that. Can't we create this
new perf_ctx_resched() to include the locking and everything. Then the
above reduces to:

if (test_bit(3, cpuc->active_mask))
perf_ctx_resched(cpuctx);

And we don't get to export the tricky bits.

> +}
> +
> +static ssize_t show_sysctl_tfa(struct device *cdev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + return snprintf(buf, 40, "%d\n", allow_tsx_force_abort);
> +}
> +
> +static ssize_t set_sysctl_tfa(struct device *cdev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + unsigned long val;
> + ssize_t ret;
> +
> + ret = kstrtoul(buf, 0, &val);

You want kstrtobool()

> + if (ret)
> + return ret;
> +
> + /* looking for boolean value */
> + if (val > 2)
> + return -EINVAL;
> +
> + /* no change */
> + if (val == allow_tsx_force_abort)
> + return count;
> +
> + allow_tsx_force_abort ^= 1;

allow_tsx_force_abort = val;

is simpler

> +
> + on_each_cpu(update_tfa_sched, NULL, 1);
> +
> + return count;
> +}

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