Re: [PATCH 2.6.9-rc2 1/2] enhanced I/O accounting data collection

[Jay Lan <jlan@engr.sgi.com>]

You are right, Jens. In our earlier posting, we also included block
device read/write counters. The block read/write counts are not very
accurate but it fits our customers' needs since they used that
information sort of for performance analysis than for accounting
purpose.

Thus the block read/write counters were removed from our patch so
that we can concentrate on the accounting needs. This bwtime (block
wait time) should have been pulled together with block read/write
counters.

Regards,
  - jay


Jens Axboe wrote:
> Hi,
> 
> 
>>Index: linux/drivers/block/ll_rw_blk.c
>>===================================================================
>>--- linux.orig/drivers/block/ll_rw_blk.c	2004-09-12 22:31:31.000000000 -0700
>>+++ linux/drivers/block/ll_rw_blk.c	2004-09-27 12:37:04.374234677 -0700
>>@@ -1741,6 +1741,7 @@
>>{
>>	DEFINE_WAIT(wait);
>>	struct request *rq;
>>+	unsigned long start_wait = jiffies;
>>
>>	generic_unplug_device(q);
>>	do {
>>@@ -1769,6 +1770,7 @@
>>		finish_wait(&rl->wait[rw], &wait);
>>	} while (!rq);
>>
>>+	current->bwtime += (unsigned long) jiffies - start_wait;
>>	return rq;
>>}
> 
> 
> What is the purpose of this hunk alone as block io accounting? It
> doesn't make any sense to me - you are accounting the time a process
> spends sleeping on a congested queue, it has nothing to do with the
> bandwidth time it used. Which, btw, isn't so easy to account on queueing
> hardware.
> 
> Just curious on what you are trying to achieve here.
>