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-rw-r--r--kernel/events/ring_buffer.c34
1 files changed, 18 insertions, 16 deletions
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index bd55ccc91373..52868716ec35 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -674,21 +674,26 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event,
if (!has_aux(event))
return -EOPNOTSUPP;
- /*
- * We need to start with the max_order that fits in nr_pages,
- * not the other way around, hence ilog2() and not get_order.
- */
- max_order = ilog2(nr_pages);
-
- /*
- * PMU requests more than one contiguous chunks of memory
- * for SW double buffering
- */
if (!overwrite) {
- if (!max_order)
- return -EINVAL;
+ /*
+ * Watermark defaults to half the buffer, and so does the
+ * max_order, to aid PMU drivers in double buffering.
+ */
+ if (!watermark)
+ watermark = nr_pages << (PAGE_SHIFT - 1);
- max_order--;
+ /*
+ * Use aux_watermark as the basis for chunking to
+ * help PMU drivers honor the watermark.
+ */
+ max_order = get_order(watermark);
+ } else {
+ /*
+ * We need to start with the max_order that fits in nr_pages,
+ * not the other way around, hence ilog2() and not get_order.
+ */
+ max_order = ilog2(nr_pages);
+ watermark = 0;
}
rb->aux_pages = kcalloc_node(nr_pages, sizeof(void *), GFP_KERNEL,
@@ -743,9 +748,6 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event,
rb->aux_overwrite = overwrite;
rb->aux_watermark = watermark;
- if (!rb->aux_watermark && !rb->aux_overwrite)
- rb->aux_watermark = nr_pages << (PAGE_SHIFT - 1);
-
out:
if (!ret)
rb->aux_pgoff = pgoff;