Drivers: hv: vmbus: Optimize vmbus_on_event

In the vmbus_on_event loop, 2 jiffies timer will not serve the purpose if
callback_fn takes longer. For effective use move this check inside of
callback functions where needed. Out of all the VMbus drivers using
vmbus_on_event, only storvsc has a high packet volume, thus add this limit
only in storvsc callback for now.
There is no apparent benefit of loop itself because this tasklet will be
scheduled anyway again if there are packets left in ring buffer. This
patch removes this unnecessary loop as well.

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1658741848-4210-1-git-send-email-ssengar@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index eca7afd366d6de0948636db918058073032c10df..9dc27e5d367a20c9bce2cb4f6253913724bf02e2 100644 (file)
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -431,34 +431,29 @@ struct vmbus_channel *relid2channel(u32 relid)
 void vmbus_on_event(unsigned long data)
 {
        struct vmbus_channel *channel = (void *) data;
-       unsigned long time_limit = jiffies + 2;
+       void (*callback_fn)(void *context);
 
        trace_vmbus_on_event(channel);
 
        hv_debug_delay_test(channel, INTERRUPT_DELAY);
-       do {
-               void (*callback_fn)(void *);
 
-               /* A channel once created is persistent even when
-                * there is no driver handling the device. An
-                * unloading driver sets the onchannel_callback to NULL.
-                */
-               callback_fn = READ_ONCE(channel->onchannel_callback);
-               if (unlikely(callback_fn == NULL))
-                       return;
-
-               (*callback_fn)(channel->channel_callback_context);
+       /* A channel once created is persistent even when
+        * there is no driver handling the device. An
+        * unloading driver sets the onchannel_callback to NULL.
+        */
+       callback_fn = READ_ONCE(channel->onchannel_callback);
+       if (unlikely(!callback_fn))
+               return;
 
-               if (channel->callback_mode != HV_CALL_BATCHED)
-                       return;
+       (*callback_fn)(channel->channel_callback_context);
 
-               if (likely(hv_end_read(&channel->inbound) == 0))
-                       return;
+       if (channel->callback_mode != HV_CALL_BATCHED)
+               return;
 
-               hv_begin_read(&channel->inbound);
-       } while (likely(time_before(jiffies, time_limit)));
+       if (likely(hv_end_read(&channel->inbound) == 0))
+               return;
 
-       /* The time limit (2 jiffies) has been reached */
+       hv_begin_read(&channel->inbound);
        tasklet_schedule(&channel->callback_event);
 }
 

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 8ced292c4b96236a96187bdd7e7fb20130f2925b..398777d3ec157b1bc705779d8dc44071fc565d7a 100644 (file)
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -60,6 +60,9 @@
 #define VMSTOR_PROTO_VERSION_WIN8_1    VMSTOR_PROTO_VERSION(6, 0)
 #define VMSTOR_PROTO_VERSION_WIN10     VMSTOR_PROTO_VERSION(6, 2)
 
+/* channel callback timeout in ms */
+#define CALLBACK_TIMEOUT               2
+
 /*  Packet structure describing virtual storage requests. */
 enum vstor_packet_operation {
        VSTOR_OPERATION_COMPLETE_IO             = 1,
@@ -1204,6 +1207,7 @@ static void storvsc_on_channel_callback(void *context)
        struct hv_device *device;
        struct storvsc_device *stor_device;
        struct Scsi_Host *shost;
+       unsigned long time_limit = jiffies + msecs_to_jiffies(CALLBACK_TIMEOUT);
 
        if (channel->primary_channel != NULL)
                device = channel->primary_channel->device_obj;
@@ -1224,6 +1228,11 @@ static void storvsc_on_channel_callback(void *context)
                u32 minlen = rqst_id ? sizeof(struct vstor_packet) :
                        sizeof(enum vstor_packet_operation);
 
+               if (unlikely(time_after(jiffies, time_limit))) {
+                       hv_pkt_iter_close(channel);
+                       return;
+               }
+
                if (pktlen < minlen) {
                        dev_err(&device->device,
                                "Invalid pkt: id=%llu, len=%u, minlen=%u\n",