Re: [PATCH v11 2/4] drm/xe: Add locks in gtidle code

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Dec 20, 2024 at 12:59:25PM -0800, Vinay Belgaumkar wrote:
> Another entry point is added so PMU code can call into the gtidle
> method for residency. Add locking so that parallel calls to this
> method from sysfs and PMU don't give inconsistent gtidle states
> for c6 residency.
> 
> Suggested-by: Lucas De Marchi <lucas.demarchi@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_gt_idle.c       | 23 ++++++++++++++++++++---
>  drivers/gpu/drm/xe/xe_gt_idle.h       |  1 +
>  drivers/gpu/drm/xe/xe_gt_idle_types.h |  3 +++
>  3 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_idle.c b/drivers/gpu/drm/xe/xe_gt_idle.c
> index fd80afeef56a..1f32ac964abe 100644
> --- a/drivers/gpu/drm/xe/xe_gt_idle.c
> +++ b/drivers/gpu/drm/xe/xe_gt_idle.c
> @@ -69,6 +69,8 @@ static u64 get_residency_ms(struct xe_gt_idle *gtidle, u64 cur_residency)
>  {
>  	u64 delta, overflow_residency, prev_residency;
>  
> +	lockdep_assert_held(&gtidle->lock);
> +
>  	overflow_residency = BIT_ULL(32);
>  
>  	/*
> @@ -273,8 +275,21 @@ static ssize_t idle_status_show(struct device *dev,
>  
>  	return sysfs_emit(buff, "%s\n", gt_idle_state_to_string(state));
>  }
> -static DEVICE_ATTR_RO(idle_status);
>  
> +u64 xe_gt_idle_residency_msec(struct xe_gt_idle *gtidle)
> +{
> +	struct xe_guc_pc *pc = gtidle_to_pc(gtidle);
> +	u64 residency;
> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&gtidle->lock, flags);

Why raw spin lock rather than just spin lock?

Matt

> +	residency = get_residency_ms(gtidle, gtidle->idle_residency(pc));
> +	raw_spin_unlock_irqrestore(&gtidle->lock, flags);
> +
> +	return residency;
> +}
> +
> +static DEVICE_ATTR_RO(idle_status);
>  static ssize_t idle_residency_ms_show(struct device *dev,
>  				      struct device_attribute *attr, char *buff)
>  {
> @@ -283,10 +298,10 @@ static ssize_t idle_residency_ms_show(struct device *dev,
>  	u64 residency;
>  
>  	xe_pm_runtime_get(pc_to_xe(pc));
> -	residency = gtidle->idle_residency(pc);
> +	residency = xe_gt_idle_residency_msec(gtidle);
>  	xe_pm_runtime_put(pc_to_xe(pc));
>  
> -	return sysfs_emit(buff, "%llu\n", get_residency_ms(gtidle, residency));
> +	return sysfs_emit(buff, "%llu\n", residency);
>  }
>  static DEVICE_ATTR_RO(idle_residency_ms);
>  
> @@ -329,6 +344,8 @@ int xe_gt_idle_init(struct xe_gt_idle *gtidle)
>  	if (!kobj)
>  		return -ENOMEM;
>  
> +	raw_spin_lock_init(&gtidle->lock);
> +
>  	if (xe_gt_is_media_type(gt)) {
>  		snprintf(gtidle->name, sizeof(gtidle->name), "gt%d-mc", gt->info.id);
>  		gtidle->idle_residency = xe_guc_pc_mc6_residency;
> diff --git a/drivers/gpu/drm/xe/xe_gt_idle.h b/drivers/gpu/drm/xe/xe_gt_idle.h
> index 4455a6501cb0..591a01e181bc 100644
> --- a/drivers/gpu/drm/xe/xe_gt_idle.h
> +++ b/drivers/gpu/drm/xe/xe_gt_idle.h
> @@ -17,5 +17,6 @@ void xe_gt_idle_disable_c6(struct xe_gt *gt);
>  void xe_gt_idle_enable_pg(struct xe_gt *gt);
>  void xe_gt_idle_disable_pg(struct xe_gt *gt);
>  int xe_gt_idle_pg_print(struct xe_gt *gt, struct drm_printer *p);
> +u64 xe_gt_idle_residency_msec(struct xe_gt_idle *gtidle);
>  
>  #endif /* _XE_GT_IDLE_H_ */
> diff --git a/drivers/gpu/drm/xe/xe_gt_idle_types.h b/drivers/gpu/drm/xe/xe_gt_idle_types.h
> index b8b297a3f884..a3667c567f8a 100644
> --- a/drivers/gpu/drm/xe/xe_gt_idle_types.h
> +++ b/drivers/gpu/drm/xe/xe_gt_idle_types.h
> @@ -6,6 +6,7 @@
>  #ifndef _XE_GT_IDLE_SYSFS_TYPES_H_
>  #define _XE_GT_IDLE_SYSFS_TYPES_H_
>  
> +#include <linux/spinlock.h>
>  #include <linux/types.h>
>  
>  struct xe_guc_pc;
> @@ -31,6 +32,8 @@ struct xe_gt_idle {
>  	u64 cur_residency;
>  	/** @prev_residency: previous residency counter */
>  	u64 prev_residency;
> +	/** @lock: Lock protecting idle residency counters */
> +	raw_spinlock_t lock;
>  	/** @idle_status: get the current idle state */
>  	enum xe_gt_idle_state (*idle_status)(struct xe_guc_pc *pc);
>  	/** @idle_residency: get idle residency counter */
> -- 
> 2.38.1
>