Hi Ming,
On 7/8/20 3:27 PM, Ming Lei wrote:
On Wed, Jul 08, 2020 at 09:58:15AM +0200, Guoqing Jiang wrote:
Currently the duration accounting of bio based driver is converted from
jiffies to ns, means it could be less accurate as request based driver.
So let disk_start_io_acct return from ns precision, instead of convert
jiffies to ns in disk_end_io_acct.
Cc: Philipp Reisner <philipp.reisner@xxxxxxxxxx>
Cc: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>
Cc: drbd-dev@xxxxxxxxxxxxxxxx
Signed-off-by: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>
---
block/blk-core.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index d9d632639bd1..0e806a8c62fb 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1466,6 +1466,7 @@ unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
struct hd_struct *part = &disk->part0;
const int sgrp = op_stat_group(op);
unsigned long now = READ_ONCE(jiffies);
+ unsigned long start_ns = ktime_get_ns();
part_stat_lock();
update_io_ticks(part, now, false);
@@ -1474,7 +1475,7 @@ unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
part_stat_local_inc(part, in_flight[op_is_write(op)]);
part_stat_unlock();
- return now;
+ return start_ns;
}
EXPORT_SYMBOL(disk_start_io_acct);
@@ -1484,11 +1485,11 @@ void disk_end_io_acct(struct gendisk *disk, unsigned int op,
struct hd_struct *part = &disk->part0;
const int sgrp = op_stat_group(op);
unsigned long now = READ_ONCE(jiffies);
- unsigned long duration = now - start_time;
+ unsigned long duration = ktime_get_ns() - start_time;
part_stat_lock();
update_io_ticks(part, now, true);
- part_stat_add(part, nsecs[sgrp], jiffies_to_nsecs(duration));
+ part_stat_add(part, nsecs[sgrp], duration);
part_stat_local_dec(part, in_flight[op_is_write(op)]);
part_stat_unlock();
Hi Guoqing,
Cost of ktime_get_ns() can be observed as not cheap in high IOPS device,
Could you share some links about it? Thanks.
so not sure the conversion is good. Also could you share what benefit we can
get with this change?
Without the conversion, we have to track io latency with jiffies in 4th
patch.
Then with HZ=100, some rows (such as 1ms, 2ms and 4ms) in that table
don't make sense.
Thanks,
Guoqing
