[Qemu-block] [PATCH 1/3] blockjob: Don't sleep meaninglessly short

[Fam Zheng]

A timer that will immediately wake the job up spoils the point to call
block_job_sleep_ns in the first place - bdrv_drain_all has to return.

Let's sleep longer to let aio_poll return, before the job resumes and
submitts more IO requests.

Signed-off-by: Fam Zheng <address@hidden>
---
 blockjob.c               | 3 ++-
 include/block/blockjob.h | 6 +++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/blockjob.c b/blockjob.c
index ba2255d..f04a16c 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -232,7 +232,8 @@ void block_job_sleep_ns(BlockJob *job, QEMUClockType type, 
int64_t ns)
     if (block_job_is_paused(job)) {
         qemu_coroutine_yield();
     } else {
-        co_aio_sleep_ns(bdrv_get_aio_context(job->bs), type, ns);
+        co_aio_sleep_ns(bdrv_get_aio_context(job->bs), type,
+                        MAX(ns, BLOCK_JOB_SLEEP_MIN));
     }
     job->busy = true;
 }
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index b6d4ebb..97835aa 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -140,11 +140,15 @@ void *block_job_create(const BlockJobDriver *driver, 
BlockDriverState *bs,
                        int64_t speed, BlockCompletionFunc *cb,
                        void *opaque, Error **errp);
 
+#define BLOCK_JOB_SLEEP_MIN 100000LL
 /**
  * block_job_sleep_ns:
  * @job: The job that calls the function.
  * @clock: The clock to sleep on.
- * @ns: How many nanoseconds to stop for.
+ * @ns: How many nanoseconds to stop for.  It would be meaningless if it is
+ * very short, because the timer to wake up the job could fire right very
+ * quickly even before anything else is done.  Hence, a minimum,
+ * BLOCK_JOB_SLEEP_MIN, is defined.
  *
  * Put the job to sleep (assuming that it wasn't canceled) for @ns
  * nanoseconds.  Canceling the job will interrupt the wait immediately.
-- 
2.1.0