bdev: stop zeroing data in spdk_bdev_get_io_stat()

This will allow multiple independent callers to request I/O statistics
without stepping on each other (previously the stats would be reset on
each request, which only works with a single caller).

This also means that we can now allow requesting stats while the VTune
integration is enabled.

Change-Id: Ia9d4d6fd37fa66b3671cd33b3183c90524f955bd
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/412257
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 ## v18.07: (Upcoming Release)
 
+### Bdev
+
+The spdk_bdev_get_io_stat() function now returns cumulative totals instead of resetting
+on each call. This allows multiple callers to query I/O statistics without conflicting
+with each other. Existing users will need to adjust their code to record the previous
+I/O statistics to calculate the delta between calls.
+
 ### git pre-commit and pre-push hooks
 
 The pre-commit hook will run `scripts/check_format.sh` and verify there are no formating

include/spdk/bdev.h

@@ -776,8 +776,7 @@ int spdk_bdev_nvme_io_passthru_md(struct spdk_bdev_desc *bdev_desc,
 int spdk_bdev_free_io(struct spdk_bdev_io *bdev_io);
 
 /**
- * Return I/O statistics for this channel. After returning stats, zero out
+ * Return I/O statistics for this channel.
- * the current state of the statistics.
  *
  * \param bdev Block device.
  * \param ch I/O channel. Obtained by calling spdk_bdev_get_io_channel().

lib/bdev/bdev.c

@@ -205,6 +205,7 @@ struct spdk_bdev_channel {
 	uint64_t		start_tsc;
 	uint64_t		interval_tsc;
 	__itt_string_handle	*handle;
+	struct spdk_bdev_io_stat prev_stat;
 #endif
 
 };
@@ -1117,6 +1118,7 @@ spdk_bdev_channel_create(void *io_device, void *ctx_buf)
 	}
 
 	memset(&ch->stat, 0, sizeof(ch->stat));
+	ch->stat.ticks_rate = spdk_get_ticks_hz();
 	ch->io_outstanding = 0;
 	TAILQ_INIT(&ch->queued_resets);
 	ch->flags = 0;
@@ -1135,6 +1137,7 @@ spdk_bdev_channel_create(void *io_device, void *ctx_buf)
 		free(name);
 		ch->start_tsc = spdk_get_ticks();
 		ch->interval_tsc = spdk_get_ticks_hz() / 100;
+		memset(&ch->prev_stat, 0, sizeof(ch->prev_stat));
 	}
 #endif
 
@@ -1961,17 +1964,9 @@ void
 spdk_bdev_get_io_stat(struct spdk_bdev *bdev, struct spdk_io_channel *ch,
 		      struct spdk_bdev_io_stat *stat)
 {
-#ifdef SPDK_CONFIG_VTUNE
-	SPDK_ERRLOG("Calling spdk_bdev_get_io_stat is not allowed when VTune integration is enabled.\n");
-	memset(stat, 0, sizeof(*stat));
-	return;
-#endif
-
 	struct spdk_bdev_channel *channel = spdk_io_channel_get_ctx(ch);
 
-	channel->stat.ticks_rate = spdk_get_ticks_hz();
 	*stat = channel->stat;
-	memset(&channel->stat, 0, sizeof(channel->stat));
 }
 
 static void
@@ -2233,17 +2228,17 @@ _spdk_bdev_io_complete(void *ctx)
 	if (now_tsc > (bdev_io->ch->start_tsc + bdev_io->ch->interval_tsc)) {
 		uint64_t data[5];
 
-		data[0] = bdev_io->ch->stat.num_read_ops;
+		data[0] = bdev_io->ch->stat.num_read_ops - bdev_io->ch->prev_stat.num_read_ops;
-		data[1] = bdev_io->ch->stat.bytes_read;
+		data[1] = bdev_io->ch->stat.bytes_read - bdev_io->ch->prev_stat.bytes_read;
-		data[2] = bdev_io->ch->stat.num_write_ops;
+		data[2] = bdev_io->ch->stat.num_write_ops - bdev_io->ch->prev_stat.num_write_ops;
-		data[3] = bdev_io->ch->stat.bytes_written;
+		data[3] = bdev_io->ch->stat.bytes_written - bdev_io->ch->prev_stat.bytes_written;
 		data[4] = bdev_io->bdev->fn_table->get_spin_time ?
 			  bdev_io->bdev->fn_table->get_spin_time(bdev_io->ch->channel) : 0;
 
 		__itt_metadata_add(g_bdev_mgr.domain, __itt_null, bdev_io->ch->handle,
 				   __itt_metadata_u64, 5, data);
 
-		memset(&bdev_io->ch->stat, 0, sizeof(bdev_io->ch->stat));
+		bdev_io->ch->prev_stat = bdev_io->ch->stat;
 		bdev_io->ch->start_tsc = now_tsc;
 	}
 #endif