Drivers: hv: Add code to distribute channel interrupt load

Implement a simple policy for distributing incoming interrupt load.
We classify channels as (a) performance critical and (b) not
performance critical. All non-performance critical channels will
be bound to the boot cpu. Performance critical channels will be
bound to the remaining available CPUs on a round-robin basis.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/channel_mgmt.c

@@ -257,6 +257,89 @@ static void vmbus_process_offer(struct work_struct *work)
 	}
 }
 
+enum {
+	IDE = 0,
+	SCSI,
+	NIC,
+	MAX_PERF_CHN,
+};
+
+/*
+ * This is an array of channels (devices) that are performance critical.
+ * We attempt to distribute the interrupt load for these devices across
+ * all available CPUs.
+ */
+static const uuid_le hp_devs[] = {
+	/* {32412632-86cb-44a2-9b5c-50d1417354f5} */
+	/* IDE */
+	{
+		.b = {
+			0x32, 0x26, 0x41, 0x32, 0xcb, 0x86, 0xa2, 0x44,
+			0x9b, 0x5c, 0x50, 0xd1, 0x41, 0x73, 0x54, 0xf5
+		}
+	},
+	/* {ba6163d9-04a1-4d29-b605-72e2ffb1dc7f} */
+	/* Storage - SCSI */
+	{
+		.b  = {
+			0xd9, 0x63, 0x61, 0xba, 0xa1, 0x04, 0x29, 0x4d,
+			0xb6, 0x05, 0x72, 0xe2, 0xff, 0xb1, 0xdc, 0x7f
+		}
+	},
+	/* {F8615163-DF3E-46c5-913F-F2D2F965ED0E} */
+	/* Network */
+	{
+		.b = {
+			0x63, 0x51, 0x61, 0xF8, 0x3E, 0xDF, 0xc5, 0x46,
+			0x91, 0x3F, 0xF2, 0xD2, 0xF9, 0x65, 0xED, 0x0E
+		}
+	},
+
+};
+
+
+/*
+ * We use this state to statically distribute the channel interrupt load.
+ */
+static u32  next_vp;
+
+/*
+ * Starting with Win8, we can statically distribute the incoming
+ * channel interrupt load by binding a channel to VCPU. We
+ * implement here a simple round robin scheme for distributing
+ * the interrupt load.
+ * We will bind channels that are not performance critical to cpu 0 and
+ * performance critical channels (IDE, SCSI and Network) will be uniformly
+ * distributed across all available CPUs.
+ */
+static u32 get_vp_index(uuid_le *type_guid)
+{
+	u32 cur_cpu;
+	int i;
+	bool perf_chn = false;
+	u32 max_cpus = num_online_cpus();
+
+	for (i = IDE; i < MAX_PERF_CHN; i++) {
+		if (!memcmp(type_guid->b, hp_devs[i].b,
+				 sizeof(uuid_le))) {
+			perf_chn = true;
+			break;
+		}
+	}
+	if ((vmbus_proto_version == VERSION_WS2008) ||
+	    (vmbus_proto_version == VERSION_WIN7) || (!perf_chn)) {
+		/*
+		 * Prior to win8, all channel interrupts are
+		 * delivered on cpu 0.
+		 * Also if the channel is not a performance critical
+		 * channel, bind it to cpu 0.
+		 */
+		return 0;
+	}
+	cur_cpu = (++next_vp % max_cpus);
+	return hv_context.vp_index[cur_cpu];
+}
+
 /*
  * vmbus_onoffer - Handler for channel offers from vmbus in parent partition.
  *
@@ -302,7 +385,7 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
 				offer->connection_id;
 	}
 
-	newchannel->target_vp = 0;
+	newchannel->target_vp = get_vp_index(&offer->offer.if_type);
 
 	memcpy(&newchannel->offermsg, offer,
 	       sizeof(struct vmbus_channel_offer_channel));