NVMe: Adhere to request queue block accounting enable/disable

Recently, a new sysfs control "iostats" was added to selectively enable or disable io statistics collection for request queues. This patch hooks that control.

IO statistics collection is rather expensive on large, multi-node machines with drives pushing millions of iops. Having the ability to disable collection if not needed can improve throughput significantly.

As a data point, on a quad E5-4640, I see more than 50% throughput improvement when io statistics accounting is disabled during heavily multi-threaded small block random read benchmarks where device performance is in the million iops+ range.

Signed-off-by Sam Bradshaw <sbradshaw at micron.com>

---

drivers/block/nvme-core.c +14 -19

index 3a25502..cd8a8bc 100644
@@ -383,30 +383,25 @@ void nvme_free_iod(struct nvme_dev *dev, struct nvme_iod *iod)
 static void nvme_start_io_acct(struct bio *bio)
 {
 	struct gendisk *disk = bio->bi_bdev->bd_disk;
-	if (blk_queue_io_stat(disk->queue)) {
-		const int rw = bio_data_dir(bio);
-		int cpu = part_stat_lock();
-		part_round_stats(cpu, &disk->part0);
-		part_stat_inc(cpu, &disk->part0, ios[rw]);
-		part_stat_add(cpu, &disk->part0, sectors[rw],
-							bio_sectors(bio));
-		part_inc_in_flight(&disk->part0, rw);
-		part_stat_unlock();
-	}
+	const int rw = bio_data_dir(bio);
+	int cpu = part_stat_lock();
+	part_round_stats(cpu, &disk->part0);
+	part_stat_inc(cpu, &disk->part0, ios[rw]);
+	part_stat_add(cpu, &disk->part0, sectors[rw], bio_sectors(bio));
+	part_inc_in_flight(&disk->part0, rw);
+	part_stat_unlock();
 }
 
 static void nvme_end_io_acct(struct bio *bio, unsigned long start_time)
 {
 	struct gendisk *disk = bio->bi_bdev->bd_disk;
-	if (blk_queue_io_stat(disk->queue)) {
-		const int rw = bio_data_dir(bio);
-		unsigned long duration = jiffies - start_time;
-		int cpu = part_stat_lock();
-		part_stat_add(cpu, &disk->part0, ticks[rw], duration);
-		part_round_stats(cpu, &disk->part0);
-		part_dec_in_flight(&disk->part0, rw);
-		part_stat_unlock();
-	}
+	const int rw = bio_data_dir(bio);
+	unsigned long duration = jiffies - start_time;
+	int cpu = part_stat_lock();
+	part_stat_add(cpu, &disk->part0, ticks[rw], duration);
+	part_round_stats(cpu, &disk->part0);
+	part_dec_in_flight(&disk->part0, rw);
+	part_stat_unlock();
 }
 
 static void bio_completion(struct nvme_queue *nvmeq, void *ctx,

The diff looks like the inverse of what you meant to send. :)

Quoted 65 lines · Sam Bradshaw

Recently, a new sysfs control "iostats" was added to selectively enable or disable io statistics collection for request queues. This patch hooks that control.

IO statistics collection is rather expensive on large, multi-node machines with drives pushing millions of iops. Having the ability to disable collection if not needed can improve throughput significantly.

As a data point, on a quad E5-4640, I see more than 50% throughput improvement when io statistics accounting is disabled during heavily multi-threaded small block random read benchmarks where device performance is in the million iops+ range.

Signed-off-by Sam Bradshaw <sbradshaw at micron.com>

---

drivers/block/nvme-core.c +14 -19

index 3a25502..cd8a8bc 100644
@@ -383,30 +383,25 @@ void nvme_free_iod(struct nvme_dev *dev, struct
 nvme_iod *iod)
 static void nvme_start_io_acct(struct bio *bio)
 {
    struct gendisk *disk = bio->bi_bdev->bd_disk;
-    if (blk_queue_io_stat(disk->queue)) {
-        const int rw = bio_data_dir(bio);
-        int cpu = part_stat_lock();
-        part_round_stats(cpu, &disk->part0);
-        part_stat_inc(cpu, &disk->part0, ios[rw]);
-        part_stat_add(cpu, &disk->part0, sectors[rw],
-                            bio_sectors(bio));
-        part_inc_in_flight(&disk->part0, rw);
-        part_stat_unlock();
-    }
+    const int rw = bio_data_dir(bio);
+    int cpu = part_stat_lock();
+    part_round_stats(cpu, &disk->part0);
+    part_stat_inc(cpu, &disk->part0, ios[rw]);
+    part_stat_add(cpu, &disk->part0, sectors[rw], bio_sectors(bio));
+    part_inc_in_flight(&disk->part0, rw);
+    part_stat_unlock();
 }
 
 static void nvme_end_io_acct(struct bio *bio, unsigned long start_time)
 {
    struct gendisk *disk = bio->bi_bdev->bd_disk;
-    if (blk_queue_io_stat(disk->queue)) {
-        const int rw = bio_data_dir(bio);
-        unsigned long duration = jiffies - start_time;
-        int cpu = part_stat_lock();
-        part_stat_add(cpu, &disk->part0, ticks[rw], duration);
-        part_round_stats(cpu, &disk->part0);
-        part_dec_in_flight(&disk->part0, rw);
-        part_stat_unlock();
-    }
+    const int rw = bio_data_dir(bio);
+    unsigned long duration = jiffies - start_time;
+    int cpu = part_stat_lock();
+    part_stat_add(cpu, &disk->part0, ticks[rw], duration);
+    part_round_stats(cpu, &disk->part0);
+    part_dec_in_flight(&disk->part0, rw);
+    part_stat_unlock();
 }
 

static void bio_completion(struct nvme_queue *nvmeq, void *ctx,