[PATCH 021/206] Staging: hv: Introduce a function to wait to drain outgoing I/O

K. Y. Srinivasan
2011-05-09T22:11:44Z

Rather than busy loop waiting to drain I/O, introduce a function
that does not burn CPU cycles waiting.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
---
drivers/staging/hv/storvsc.c | 6 +++++-
drivers/staging/hv/storvsc_api.h | 12 ++++++++++++
2 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/drivers/staging/hv/storvsc.c b/drivers/staging/hv/storvsc.c
index 8ee1ad0..36458b8 100644
--- a/drivers/staging/hv/storvsc.c
+++ b/drivers/staging/hv/storvsc.c
@@ -47,6 +47,7 @@ static inline struct storvsc_device *alloc_stor_device(struct hv_device *device)
/* (ie get_stor_device() and must_get_stor_device()) to proceed. */
atomic_cmpxchg(&stor_device->ref_count, 0, 2);

+ init_waitqueue_head(&stor_device->waiting_to_drain);
stor_device->device = device;
device->ext = stor_device;

@@ -332,7 +333,10 @@ static void stor_vsc_on_io_completion(struct hv_device *device,

request->on_io_completion(request);

- atomic_dec(&stor_device->num_outstanding_req);
+ if (atomic_dec_and_test(&stor_device->num_outstanding_req) &&
+ stor_device->drain_notify)
+ wake_up(&stor_device->waiting_to_drain);
+

put_stor_device(device);
}
diff --git a/drivers/staging/hv/storvsc_api.h b/drivers/staging/hv/storvsc_api.h
index 32228c0..1887940 100644
--- a/drivers/staging/hv/storvsc_api.h
+++ b/drivers/staging/hv/storvsc_api.h
@@ -26,6 +26,7 @@
#define _STORVSC_API_H_

#include <linux/kernel.h>
+#include <linux/wait.h>
#include "vstorage.h"
#include "vmbus_api.h"
#include "vmbus.h"
@@ -108,8 +109,11 @@ struct storvsc_device {
/* 0 indicates the device is being destroyed */
atomic_t ref_count;

+ bool drain_notify;
atomic_t num_outstanding_req;

+ wait_queue_head_t waiting_to_drain;
+
/*
* Each unique Port/Path/Target represents 1 channel ie scsi
* controller. In reality, the pathid, targetid is always 0
@@ -161,6 +165,14 @@ struct storvsc_driver *drv_to_stordrv(struct device_driver *d)
return hvdr_to_stordr(hvdrv);
}

+static inline void storvsc_wait_to_drain(struct storvsc_device *dev)
+{
+ dev->drain_notify = true;
+ wait_event(dev->waiting_to_drain,
+ atomic_read(&dev->num_outstanding_req) == 0);
+ dev->drain_notify = false;
+}
+
/* Interface */

int storvsc_dev_add(struct hv_device *device,
--
1.7.4.1