blockjob: Adhere to rate limit even when reentered early

When jobs are sleeping, for example to enforce a given rate limit, they
can be reentered early, in particular in order to get paused, to update
the rate limit or to get cancelled.

Before this patch, they behave in this case as if they had fully
completed their rate limiting delay. This means that requests are sped
up beyond their limit, violating the constraints that the user gave us.

Change the block jobs to sleep in a loop until the necessary delay is
completed, while still allowing cancelling them immediately as well
pausing (handled by the pause point in job_sleep_ns()) and updating the
rate limit.

This change is also motivated by iotests cases being prone to fail
because drain operations pause and unpause them so often that block jobs
complete earlier than they are supposed to. In particular, the next
commit would fail iotests 030 without this change.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230510203601.418015-8-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 20 insertions, 2 deletions

diff --git a/blockjob.c b/blockjob.c
index 659c3cb9de..913da3cbf7 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -319,10 +319,28 @@ static bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
     return block_job_set_speed_locked(job, speed, errp);
 }
 
-int64_t block_job_ratelimit_get_delay(BlockJob *job, uint64_t n)
+void block_job_ratelimit_processed_bytes(BlockJob *job, uint64_t n)
 {
     IO_CODE();
-    return ratelimit_calculate_delay(&job->limit, n);
+    ratelimit_calculate_delay(&job->limit, n);
+}
+
+void block_job_ratelimit_sleep(BlockJob *job)
+{
+    uint64_t delay_ns;
+
+    /*
+     * Sleep at least once. If the job is reentered early, keep waiting until
+     * we've waited for the full time that is necessary to keep the job at the
+     * right speed.
+     *
+     * Make sure to recalculate the delay after each (possibly interrupted)
+     * sleep because the speed can change while the job has yielded.
+     */
+    do {
+        delay_ns = ratelimit_calculate_delay(&job->limit, 0);
+        job_sleep_ns(&job->job, delay_ns);
+    } while (delay_ns && !job_is_cancelled(&job->job));
 }
 
 BlockJobInfo *block_job_query_locked(BlockJob *job, Error **errp)