Re: [Patch for review] BSD accounting IO stats

[Guillaume Thouvenin]

Andi Kleen wrote:

> > diff -uprN -X dontdiff linux-2.6.8-rc2/drivers/block/ll_rw_blk.c linux-2.6.8-rc2+BSDacct_IO/drivers/block/ll_rw_blk.c
> > --- linux-2.6.8-rc2/drivers/block/ll_rw_blk.c	2004-07-18 06:57:42.000000000 +0200
> > +++ linux-2.6.8-rc2+BSDacct_IO/drivers/block/ll_rw_blk.c	2004-07-27 09:17:33.149321480 +0200
> > @@ -1949,10 +1949,12 @@ void drive_stat_acct(struct request *rq,
> >
> > 	if (rw == READ) {
> > 		disk_stat_add(rq->rq_disk, read_sectors, nr_sectors);
> > +		current->rblk += nr_sectors;
> >    
>
> This doesn't look very useful, because most writes which
> are flushed delayed would get accounted to pdflushd.
> Using such inaccurate data for accounting sounds quite dangerous
> to me.
>  
I agree with that. Like you and Andrew said, this metric (write block) 
is just an estimate (quite wrong indeed) of what really occurred in the 
system because some writings are accounted elsewhere (pdflush or 
journaling file system).

I also agree that a rough estimation is not very interesting, therefore 
I'm working on another patch to provide accurate values.

Best,
Guillaume
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