[PATCH 1/3] drm/xe/gt_stats: Detect and log overflow

[Lucas De Marchi]

On Tue, Feb 25, 2025 at 02:17:04PM +0100, Francois Dugast wrote:
>Check if the atomic counter limit has been reached and if that is the
>case, set the counter value to the new increment to prevent keeping
>a garbage value, and notify it in the kernel log as below:
>
>    [drm:xe_gt_stats_incr [xe]] GT0: stats vma_pagefault_bytes overflow, resetting
>
>Signed-off-by: Francois Dugast <francois.dugast at intel.com>
>---
> drivers/gpu/drm/xe/xe_gt_stats.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/gpu/drm/xe/xe_gt_stats.c b/drivers/gpu/drm/xe/xe_gt_stats.c
>index 2e9879ea4674..753c081b68a6 100644
>--- a/drivers/gpu/drm/xe/xe_gt_stats.c
>+++ b/drivers/gpu/drm/xe/xe_gt_stats.c
>@@ -8,8 +8,15 @@
> #include <drm/drm_print.h>
>
> #include "xe_gt.h"
>+#include "xe_gt_printk.h"
> #include "xe_gt_stats.h"
>
>+static const char *const stat_description[__XE_GT_STATS_NUM_IDS] = {
>+	"tlb_inval_count",
>+	"vma_pagefault_count",
>+	"vma_pagefault_bytes",
>+};
>+
> /**
>  * xe_gt_stats_incr - Increments the specified stats counter
>  * @gt: GT structure
>@@ -24,13 +31,12 @@ void xe_gt_stats_incr(struct xe_gt *gt, const enum xe_gt_stats_id id, int incr)
> 		return;
>
> 	atomic_add(incr, &gt->stats.counters[id]);
>-}
>
>-static const char *const stat_description[__XE_GT_STATS_NUM_IDS] = {
>-	"tlb_inval_count",
>-	"vma_pagefault_count",
>-	"vma_pagefault_bytes",
>-};
>+	if (atomic_read(&gt->stats.counters[id]) < 0) {

why are we not using unsigned logic? it stops being atomic when you
update/read/set.

Lucas De Marchi

>+		xe_gt_dbg(gt, "stats %s overflow, resetting\n", stat_description[id]);
>+		atomic_set(&gt->stats.counters[id], incr);
>+	}
>+}
>
> /**
>  * xe_gt_stats_print_info - Print the GT stats
>-- 
>2.43.0
>