[PATCH v1 3/5] powerpc/pseries: Fix stolen time accounting when dtl debugfs is used

[Naveen N. Rao]

When the dtl debugfs interface is used, we usually set the
dtl_enable_mask to 0x7 (DTL_LOG_ALL). When this happens, we start seeing
DTL entries for all preempt reasons, including CEDE. In
scan_dispatch_log(), we add up the times from all entries and account
those towards stolen time. However, we should only be accounting stolen
time when the preemption was due to HDEC at the end of our time slice.

Fix this by checking for the dispatch reason in the DTL entry before
adding to the stolen time.

Fixes: cf9efce0ce313 ("powerpc: Account time using timebase rather than PURR")
Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
---
 arch/powerpc/kernel/time.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 40868f3ee113..923abc3e555d 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -199,7 +199,7 @@ static u64 scan_dispatch_log(u64 stop_tb)
 	struct lppaca *vpa = local_paca->lppaca_ptr;
 	u64 tb_delta;
 	u64 stolen = 0;
-	u64 dtb;
+	u64 dtb, dispatch_reason;
 
 	if (!dtl)
 		return 0;
@@ -210,6 +210,7 @@ static u64 scan_dispatch_log(u64 stop_tb)
 		dtb = be64_to_cpu(dtl->timebase);
 		tb_delta = be32_to_cpu(dtl->enqueue_to_dispatch_time) +
 			be32_to_cpu(dtl->ready_to_enqueue_time);
+		dispatch_reason = dtl->dispatch_reason;
 		barrier();
 		if (i + N_DISPATCH_LOG < be64_to_cpu(vpa->dtl_idx)) {
 			/* buffer has overflowed */
@@ -221,7 +222,9 @@ static u64 scan_dispatch_log(u64 stop_tb)
 			break;
 		if (dtl_consumer)
 			dtl_consumer(dtl, i);
-		stolen += tb_delta;
+		/* 7 indicates that this dispatch follows a time slice preempt */
+		if (dispatch_reason == 7)
+			stolen += tb_delta;
 		++i;
 		++dtl;
 		if (dtl == dtl_end)
-- 
2.19.1