[PATCH v2] powerpc/pseries/vas: Use usleep_range() to support HCALL delay

[Haren Myneni]

VAS allocate, modify and deallocate HCALLs returns
H_LONG_BUSY_ORDER_1_MSEC or H_LONG_BUSY_ORDER_10_MSEC for busy
delay and expects OS to reissue HCALL after that delay. But using
msleep() will often sleep at least 20 msecs even though the
hypervisor expects to reissue these HCALLs after 1 or 10msecs.
It might cause these HCALLs takes longer when multiple threads
issue open or close VAS windows simultaneously.

So instead of msleep(), use usleep_range() to ensure sleep with
the expected value before issuing HCALL again.

Signed-off-by: Haren Myneni <haren at linux.ibm.com>
Suggested-by: Nathan Lynch <nathanl at linux.ibm.com>

---
v1 -> v2:
- Use usleep_range instead of using RTAS sleep routine as
  suggested by Nathan
---
 arch/powerpc/platforms/pseries/vas.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
index 71d52a670d95..bade4402741f 100644
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -36,9 +36,31 @@ static bool migration_in_progress;
 
 static long hcall_return_busy_check(long rc)
 {
+	unsigned int ms;
+
 	/* Check if we are stalled for some time */
 	if (H_IS_LONG_BUSY(rc)) {
-		msleep(get_longbusy_msecs(rc));
+		ms = get_longbusy_msecs(rc);
+		/*
+		 * Allocate, Modify and Deallocate HCALLs returns
+		 * H_LONG_BUSY_ORDER_1_MSEC or H_LONG_BUSY_ORDER_10_MSEC
+		 * for the long delay. So the delay should always be 1
+		 * or 10msecs, but sleeps 1msec in case if the long
+		 * delay is > H_LONG_BUSY_ORDER_10_MSEC.
+		 */
+		if (ms > 10)
+			ms = 1;
+
+		/*
+		 * msleep() will often sleep at least 20 msecs even
+		 * though the hypervisor expects to reissue these
+		 * HCALLs after 1 or 10msecs. So use usleep_range()
+		 * to sleep with the expected value.
+		 *
+		 * See Documentation/timers/timers-howto.rst on using
+		 * the value range in usleep_range().
+		 */
+		usleep_range(ms * 100, ms * 1000);
 		rc = H_BUSY;
 	} else if (rc == H_BUSY) {
 		cond_resched();
-- 
2.26.3