From: Qiang Liu <redacted>
Balloon inflate/deflate block in tell_host() for host buffer consumption.
Host-side stalls are easily mistaken for guest allocation issues.
Add virtio_balloon_host_ack to record tell_host() wait time,
virtqueue and PFN count, to split balloon latency between guest and host.
Signed-off-by: Qiang Liu <redacted>
---
drivers/virtio/virtio_balloon.c | 19 +++++++++++++++++--
include/trace/events/virtio_balloon.h | 22 ++++++++++++++++++++++
2 files changed, 39 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 2d0b16383661..c4fdc6815b41 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -19,6 +19,7 @@
#include <linux/wait.h>
#include <linux/mm.h>
#include <linux/page_reporting.h>
+#include <linux/ktime.h>
#define CREATE_TRACE_POINTS
#include <trace/events/virtio_balloon.h>
@@ -197,8 +198,22 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
return;
virtqueue_kick(vq);
- /* When host has read buffer, this completes via balloon_ack */
- wait_event(vb->acked, virtqueue_get_buf(vq, &len));
+ /*
+ * When host has read buffer, this completes via balloon_ack.
+ *
+ * The latency is only measured when the tracepoint is enabled, so a
+ * disabled tracepoint adds no clock reads on this (hot) path.
+ */
+ if (trace_virtio_balloon_host_ack_enabled()) {
+ ktime_t start = ktime_get();
+
+ wait_event(vb->acked, virtqueue_get_buf(vq, &len));
+ trace_virtio_balloon_host_ack(vb->num_pfns,
+ vq->name,
+ ktime_to_ns(ktime_sub(ktime_get(), start)));
+ } else {
+ wait_event(vb->acked, virtqueue_get_buf(vq, &len));
+ }
}
static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info,diff --git a/include/trace/events/virtio_balloon.h b/include/trace/events/virtio_balloon.h
index f733fc360d8b..559deb997e88 100644
--- a/include/trace/events/virtio_balloon.h
+++ b/include/trace/events/virtio_balloon.h
@@ -81,6 +81,28 @@ TRACE_EVENT(virtio_balloon_deflate,
__entry->requested, __entry->deflated, __entry->num_pages)
);
+TRACE_EVENT(virtio_balloon_host_ack,
+
+ TP_PROTO(unsigned int num_pfns, const char *vq_name, s64 latency_ns),
+
+ TP_ARGS(num_pfns, vq_name, latency_ns),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, num_pfns)
+ __string(vq_name, vq_name)
+ __field(s64, latency_ns)
+ ),
+
+ TP_fast_assign(
+ __entry->num_pfns = num_pfns;
+ __assign_str(vq_name);
+ __entry->latency_ns = latency_ns;
+ ),
+
+ TP_printk("vq=%s num_pfns=%u latency=%lldns",
+ __get_str(vq_name), __entry->num_pfns, __entry->latency_ns)
+);
+
#endif /* _TRACE_VIRTIO_BALLOON_H */
/* This part must be outside protection */--
2.43.0
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