[gve] Increase number of receive buffers to reduce packet loss

Experiments suggest that using fewer than 64 receive buffers leads to
excessive packet drop rates on some instance types (observed with a
c3-standard-4 instance in europe-west4-a).

Fix by increasing the number of receive data buffers (and adjusting
the length of the registrable queue page address list to match).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

2 files changed, 13 insertions, 5 deletions

diff --git a/src/drivers/net/gve.c b/src/drivers/net/gve.c
index 03edc0899..7f86dd219 100644
--- a/src/drivers/net/gve.c
+++ b/src/drivers/net/gve.c
@@ -722,6 +722,7 @@ static int gve_alloc_qpl ( struct gve_nic *gve, struct gve_qpl *qpl,
 	/* Calculate number of pages required */
 	build_assert ( GVE_BUF_SIZE <= GVE_PAGE_SIZE );
 	qpl->count = ( ( buffers + GVE_BUF_PER_PAGE - 1 ) / GVE_BUF_PER_PAGE );
+	assert ( qpl->count <= GVE_QPL_MAX );
 
 	/* Allocate pages (as a single block) */
 	len = ( qpl->count * GVE_PAGE_SIZE );
diff --git a/src/drivers/net/gve.h b/src/drivers/net/gve.h
index 2845699ac..247d6e699 100644
--- a/src/drivers/net/gve.h
+++ b/src/drivers/net/gve.h
@@ -59,9 +59,6 @@ struct google_mac {
  */
 #define GVE_LEN_ALIGN 64
 
-/** Maximum number of pages per queue (must be a power of two) */
-#define GVE_QPL_MAX 16
-
 /** Configuration BAR */
 #define GVE_CFG_BAR PCI_BASE_ADDRESS_0
 
@@ -208,6 +205,14 @@ struct gve_admin_register {
 	uint64_t size;
 } __attribute__ (( packed ));
 
+/**
+ * Maximum number of pages per queue
+ *
+ * This is a policy decision.  Must be sufficient to allow for both
+ * the transmit and receive queue fill levels.
+ */
+#define GVE_QPL_MAX 32
+
 /** Page list */
 struct gve_pages {
 	/** Page address */
@@ -538,9 +543,11 @@ struct gve_tx_descriptor {
 /**
  * Maximum number of receive buffers
  *
- * This is a policy decision.
+ * This is a policy decision.  Experiments suggest that using fewer
+ * than 64 receive buffers leads to excessive packet drop rates on
+ * some instance types.
  */
-#define GVE_RX_FILL 16
+#define GVE_RX_FILL 64
 
 /** Receive queue page list ID */
 #define GVE_RX_QPL 0x18ae5258