Re: [PATCH] md: don't account io stat for split bio

[Guoqing Jiang <jgq516@gmail.com>]

On 5/11/21 3:10 PM, Christoph Hellwig wrote:
> On Mon, May 10, 2021 at 11:58:32PM -0700, Song Liu wrote:
>> IIUC, the sysfs node is needed to get better performance (by disabling
>> accounting)?
> FYI, we already have that sysfs file in the block layer
> ("queue/iostats"), please just observe QUEUE_FLAG_IO_STAT flag.

Seems only nvdimm observe the flag before call bio_{start,end}_io_acct.
Does it make sense to make the checking mandatory? Something like.

--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1315,6 +1315,9 @@ static unsigned long __part_start_io_acct(struct 
block_device *part,
         const int sgrp = op_stat_group(op);
         unsigned long now = READ_ONCE(jiffies);

+       if (!blk_queue_io_stat(part->bd_disk->queue))
+               return 0;
+
         part_stat_lock();
         update_io_ticks(part, now, false);
         part_stat_inc(part, ios[sgrp]);
@@ -1351,6 +1354,9 @@ static void __part_end_io_acct(struct block_device 
*part, unsigned int op,
         unsigned long now = READ_ONCE(jiffies);
         unsigned long duration = now - start_time;

+       if (!blk_queue_io_stat(part->bd_disk->queue))
+               return;
+

Thanks,
Guoqing