Andrew Morton <akpm@zip.com.au> writes:
> Zlatko Calusic wrote:
> >
> > Hi!
> >
> > My apologies if this is an FAQ, and I'm still catching up with
> > the linux-kernel list.
> >
> > Today I decided to convert my /tmp partition to be mounted in
> > writeback mode, as I noticed that ext3 in ordered mode syncs every 5
> > seconds and that is something defenitely not needed for /tmp, IMHO.
> >
> > Then I did some tests in order to prove my theory. :)
> >
> > But, alas, writeback is slower.
> >
>
> I cannot reproduce this. Using http://www.zip.com.au/~akpm/writer.c
>
> ext2: 0.03s user 1.43s system 97% cpu 1.501 total
> ext3 writeback: 0.02s user 2.33s system 96% cpu 2.431 total
> ext3 ordered: 0.02s user 2.52s system 98% cpu 2.574 total
>
Hm, at first I got exactly the same results for writeback/ordered
cases, as you did above, so my theory fell on the ground.
Later, bloody thing resurected again. Something really fishy is goin'
on here...
{atlas} [/mnt]# time ~zcalusic/try/awriter
~zcalusic/try/awriter 0.07s user 3.50s system 99% cpu 3.594 total
{atlas} [/mnt]# cd /tmp
{atlas} [/tmp]# time ~zcalusic/try/awriter
~zcalusic/try/awriter 0.00s user 6.05s system 98% cpu 6.129 total
{atlas} [/tmp]# mount | egrep '/tmp|/mnt'
/dev/hde2 on /tmp type ext3 (rw,data=writeback)
/dev/hde3 on /mnt type ext3 (rw)
So /tmp is writeback and /mnt is ordered (doublechecked!). See for
yourself how ext3 is slower in writeback mode. awriter is your
small program, of course.
Just for the record, I mke2fs-ed /dev/hde3 again and made it pure
ext2.
{atlas} [~]# mount | grep '/mnt'
/dev/hde3 on /mnt type ext2 (rw)
{atlas} [~]# cd /mnt
{atlas} [/mnt]# time ~zcalusic/try/awriter
~zcalusic/try/awriter 0.01s user 1.86s system 98% cpu 1.893 total
To sumarize:
ext2 0.01s user 1.86s system 98% cpu 1.893 total
ext3/ordered 0.07s user 3.50s system 99% cpu 3.594 total
ext3/writeback 0.00s user 6.05s system 98% cpu 6.129 total
What is strange is that not always I've been able to get different
results for writeback case (comparing to ordered), but when I get it,
it is repeatable.
This is a SMP machine, if that makes any difference.
Regards,
-- Zlatko - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Sat Dec 15 2001 - 21:00:15 EST