linux-kernel - [PATCH V4 4/4] scsi: storvsc: Tighten up the interrupt path

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Message-Id: <1450905351-9538-4-git-send-email-kys@microsoft.com>
Date:	Wed, 23 Dec 2015 13:15:51 -0800
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, ohering@...e.com,
	jbottomley@...allels.com, hch@...radead.org,
	linux-scsi@...r.kernel.org, apw@...onical.com, vkuznets@...hat.com,
	jasowang@...hat.com, martin.petersen@...cle.com, hare@...e.de
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH V4 4/4] scsi: storvsc: Tighten up the interrupt path

On the interrupt path, we repeatedly establish the pointer to the
storvsc_device. While the compiler does inline
get_in_stor_device() (and other static functions) in the call chain
in the interrupt path, the compiler is repeatedly inlining
the call to get_in_stor_device() each time it is invoked.
The return value of get_in_stor_device() can be cached in the
interrupt path since there is higher level serialization in
place to ensure correct handling when the module unload races
with the processing of an incoming message from the host.
Optimize this code path by caching the pointer to storvsc_device
and passing it as an argument.

Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
Reviewed-by: Long Li <longli@...rosoft.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
Reviewed-by: Hannes Reinecke <hare@...e.com>
Tested-by: Alex Ng <alexng@...rosoft.com>
---
	Added Reviewed-by: Hannes Reinecke <hare@...e.com>
	Added additional details to the commit log - James Bottomley <James.Bottomley@...senPartnership.com>
 
 drivers/scsi/storvsc_drv.c |   23 ++++++++---------------
 1 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 811f276..41c115c 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -945,19 +945,16 @@ static void storvsc_handle_error(struct vmscsi_request *vm_srb,
 }
 
 
-static void storvsc_command_completion(struct storvsc_cmd_request *cmd_request)
+static void storvsc_command_completion(struct storvsc_cmd_request *cmd_request,
+				       struct storvsc_device *stor_dev)
 {
 	struct scsi_cmnd *scmnd = cmd_request->cmd;
-	struct hv_host_device *host_dev = shost_priv(scmnd->device->host);
 	struct scsi_sense_hdr sense_hdr;
 	struct vmscsi_request *vm_srb;
 	struct Scsi_Host *host;
-	struct storvsc_device *stor_dev;
-	struct hv_device *dev = host_dev->dev;
 	u32 payload_sz = cmd_request->payload_sz;
 	void *payload = cmd_request->payload;
 
-	stor_dev = get_in_stor_device(dev);
 	host = stor_dev->host;
 
 	vm_srb = &cmd_request->vstor_packet.vm_srb;
@@ -987,14 +984,13 @@ static void storvsc_command_completion(struct storvsc_cmd_request *cmd_request)
 		kfree(payload);
 }
 
-static void storvsc_on_io_completion(struct hv_device *device,
+static void storvsc_on_io_completion(struct storvsc_device *stor_device,
 				  struct vstor_packet *vstor_packet,
 				  struct storvsc_cmd_request *request)
 {
-	struct storvsc_device *stor_device;
 	struct vstor_packet *stor_pkt;
+	struct hv_device *device = stor_device->device;
 
-	stor_device = hv_get_drvdata(device);
 	stor_pkt = &request->vstor_packet;
 
 	/*
@@ -1049,7 +1045,7 @@ static void storvsc_on_io_completion(struct hv_device *device,
 	stor_pkt->vm_srb.data_transfer_length =
 	vstor_packet->vm_srb.data_transfer_length;
 
-	storvsc_command_completion(request);
+	storvsc_command_completion(request, stor_device);
 
 	if (atomic_dec_and_test(&stor_device->num_outstanding_req) &&
 		stor_device->drain_notify)
@@ -1058,21 +1054,19 @@ static void storvsc_on_io_completion(struct hv_device *device,
 
 }
 
-static void storvsc_on_receive(struct hv_device *device,
+static void storvsc_on_receive(struct storvsc_device *stor_device,
 			     struct vstor_packet *vstor_packet,
 			     struct storvsc_cmd_request *request)
 {
 	struct storvsc_scan_work *work;
-	struct storvsc_device *stor_device;
 
 	switch (vstor_packet->operation) {
 	case VSTOR_OPERATION_COMPLETE_IO:
-		storvsc_on_io_completion(device, vstor_packet, request);
+		storvsc_on_io_completion(stor_device, vstor_packet, request);
 		break;
 
 	case VSTOR_OPERATION_REMOVE_DEVICE:
 	case VSTOR_OPERATION_ENUMERATE_BUS:
-		stor_device = get_in_stor_device(device);
 		work = kmalloc(sizeof(struct storvsc_scan_work), GFP_ATOMIC);
 		if (!work)
 			return;
@@ -1083,7 +1077,6 @@ static void storvsc_on_receive(struct hv_device *device,
 		break;
 
 	case VSTOR_OPERATION_FCHBA_DATA:
-		stor_device = get_in_stor_device(device);
 		cache_wwn(stor_device, vstor_packet);
 #if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
 		fc_host_node_name(stor_device->host) = stor_device->node_name;
@@ -1133,7 +1126,7 @@ static void storvsc_on_channel_callback(void *context)
 					vmscsi_size_delta));
 				complete(&request->wait_event);
 			} else {
-				storvsc_on_receive(device,
+				storvsc_on_receive(stor_device,
 						(struct vstor_packet *)packet,
 						request);
 			}
-- 
1.7.4.1

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