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authorFrancesco Pollicino <fra.fra.800@gmail.com>2019-03-12 09:59:33 +0100
committerJens Axboe <axboe@kernel.dk>2019-04-01 16:15:40 +0200
commit1e66413c4f68e2a61a210e4f5ff5df7a2ab86a5b (patch)
tree49e5f455fa84648d09b82a92e114dfb6975adaca
parentblock, bfq: always protect newly-created queues from existing active queues (diff)
downloadlinux-1e66413c4f68e2a61a210e4f5ff5df7a2ab86a5b.tar.xz
linux-1e66413c4f68e2a61a210e4f5ff5df7a2ab86a5b.zip
block, bfq: print SHARED instead of pid for shared queues in logs
The function "bfq_log_bfqq" prints the pid of the process associated with the queue passed as input. Unfortunately, if the queue is shared, then more than one process is associated with the queue. The pid that gets printed in this case is the pid of one of the associated processes. Which process gets printed depends on the exact sequence of merge events the queue underwent. So printing such a pid is rather useless and above all is often rather confusing because it reports a random pid between those of the associated processes. This commit addresses this issue by printing SHARED instead of a pid if the queue is shared. Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com> Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name> Signed-off-by: Francesco Pollicino <fra.fra.800@gmail.com> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/bfq-iosched.c10
-rw-r--r--block/bfq-iosched.h23
2 files changed, 29 insertions, 4 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 49bde428f7f2..37cc8f127cf6 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2590,6 +2590,16 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
* assignment causes no harm).
*/
new_bfqq->bic = NULL;
+ /*
+ * If the queue is shared, the pid is the pid of one of the associated
+ * processes. Which pid depends on the exact sequence of merge events
+ * the queue underwent. So printing such a pid is useless and confusing
+ * because it reports a random pid between those of the associated
+ * processes.
+ * We mark such a queue with a pid -1, and then print SHARED instead of
+ * a pid in logging messages.
+ */
+ new_bfqq->pid = -1;
bfqq->bic = NULL;
/* release process reference to bfqq */
bfq_put_queue(bfqq);
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 829730b96fb2..67e63c276c7a 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -32,6 +32,8 @@
#define BFQ_DEFAULT_GRP_IOPRIO 0
#define BFQ_DEFAULT_GRP_CLASS IOPRIO_CLASS_BE
+#define MAX_PID_STR_LENGTH 12
+
/*
* Soft real-time applications are extremely more latency sensitive
* than interactive ones. Over-raise the weight of the former to
@@ -1016,13 +1018,23 @@ void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq);
/* --------------- end of interface of B-WF2Q+ ---------------- */
/* Logging facilities. */
+static inline void bfq_pid_to_str(int pid, char *str, int len)
+{
+ if (pid != -1)
+ snprintf(str, len, "%d", pid);
+ else
+ snprintf(str, len, "SHARED-");
+}
+
#ifdef CONFIG_BFQ_GROUP_IOSCHED
struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
#define bfq_log_bfqq(bfqd, bfqq, fmt, args...) do { \
+ char pid_str[MAX_PID_STR_LENGTH]; \
+ bfq_pid_to_str((bfqq)->pid, pid_str, MAX_PID_STR_LENGTH); \
blk_add_cgroup_trace_msg((bfqd)->queue, \
bfqg_to_blkg(bfqq_group(bfqq))->blkcg, \
- "bfq%d%c " fmt, (bfqq)->pid, \
+ "bfq%s%c " fmt, pid_str, \
bfq_bfqq_sync((bfqq)) ? 'S' : 'A', ##args); \
} while (0)
@@ -1033,10 +1045,13 @@ struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
#else /* CONFIG_BFQ_GROUP_IOSCHED */
-#define bfq_log_bfqq(bfqd, bfqq, fmt, args...) \
- blk_add_trace_msg((bfqd)->queue, "bfq%d%c " fmt, (bfqq)->pid, \
+#define bfq_log_bfqq(bfqd, bfqq, fmt, args...) do { \
+ char pid_str[MAX_PID_STR_LENGTH]; \
+ bfq_pid_to_str((bfqq)->pid, pid_str, MAX_PID_STR_LENGTH); \
+ blk_add_trace_msg((bfqd)->queue, "bfq%s%c " fmt, pid_str, \
bfq_bfqq_sync((bfqq)) ? 'S' : 'A', \
- ##args)
+ ##args); \
+} while (0)
#define bfq_log_bfqg(bfqd, bfqg, fmt, args...) do {} while (0)
#endif /* CONFIG_BFQ_GROUP_IOSCHED */