Re: Boot speed/mount time regression with 3.4.0-rc2

[Josef Bacik <josef@redhat.com>]

On Thu, Apr 12, 2012 at 11:22:51AM +0200, Ahmet Inan wrote:
> On Wed, Apr 11, 2012 at 7:04 PM, Josef Bacik <josef@redhat.com> wrote=
:
> > On Wed, Apr 11, 2012 at 05:26:29PM +0200, Ahmet Inan wrote:
> >> On Tue, Apr 10, 2012 at 5:16 PM, Josef Bacik <josef@redhat.com> wr=
ote:
> >> > On Mon, Apr 09, 2012 at 05:20:46PM -0400, Calvin Walton wrote:
> >> >> On Mon, 2012-04-09 at 16:54 -0400, Josef Bacik wrote:
> >> >> > On Mon, Apr 09, 2012 at 01:10:04PM -0400, Calvin Walton wrote=
:
> >> >> > > On Mon, 2012-04-09 at 11:53 -0400, Calvin Walton wrote:
> >> >> > > > Hi,
> >> >> > > >
> >> >> > > > I have a system that's using a dracut-generated initramfs=
 to mount a
> >> >> > > > btrfs root. After upgrading to kernel 3.4.0-rc2 to test i=
t out, I've
> >> >> > > > noticed that the process of mounting the root filesystem =
takes much
> >> >> > > > longer with 3.4.0-rc2 than it did with 3.3.1 - nearly 30 =
seconds slower!
> >> >>
> >> >> > > And the bisect results are in:
> >> >> > > 285ff5af6ce358e73f53b55c9efadd4335f4c2ff is the first bad c=
ommit
> >> >> > > commit 285ff5af6ce358e73f53b55c9efadd4335f4c2ff
> >> >> > > Author: Josef Bacik <josef@redhat.com>
> >> >> > > Date: =A0 Fri Jan 13 15:27:45 2012 -0500
> >> >> > >
> >> >> > > =A0 =A0 Btrfs: remove the ideal caching code>
> >> >> >
> >> >> > Ok can you give this a whirl? =A0You are going to have to boo=
t/reboot a few times
> >> >> > to let the cache get re-generated again to make sure it's tak=
en effect, but
> >> >> > hopefully this will help out. =A0Thanks,
> >> >>
> >> >> Unfortunately, it doesn't seem to help. Even after 3 or 4 reboo=
ts with
> >> >> this patch applied I'm still seeing the same delay.
> >> >>
> >> >
> >> > Ok drop that previous patch and give this one a whirl, it helped=
 on my laptop.
> >> > This is only =A0half of the problem AFAICS, but it's the easier =
half to fix, in
> >> > the meantime I need to lock down why we're not writing out cache=
 for a bunch of
> >> > block groups, but thats trickier since the messages I need are s=
pit out while
> >> > I'm shutting down, so I need to get creative. =A0Let me know if/=
how much this
> >> > helps. =A0Thanks,
> >>
> >> i have tried your patch and my system still needs several minutes =
to boot
> >> until it can be used.
> >> Also tried to reboot several times - it doesn't look like its gett=
ing better.
> >> The last thing the system does when its shutting down is a read-on=
ly
> >> remount of "/" so no umount.
> >> Booting was much faster before i pulled for-linus a few weeks ago =
but
> >> i couldn't find the time to bisect it yet ..
> >>
> >> please also look at the attached dmesg.txt.
> >> this is an core i3 system with 2x2TB BTRFS RAID1 and lots of
> >> home directories and snapshots.
> >>
> >> I'm going to test this patch on twenty more computers but with
> >> smaller HDDs and less files and see if it helps to speed up their
> >> boot times.
> >>
> >
> > Ok looks like you are running into a different problem. =A0Could yo=
u maybe run
> > bootchart and upload the resulting png somewhere so I can look and =
see what all
> > is running while you boot? =A0Thanks,
>=20
> http://aam.mathematik.uni-freiburg.de/IAM/homepages/ainan/bootchart.p=
ng
>=20
> i have tried your patch now on the twenty more computers i mentioned =
and
> still it takes a minute to remount rw "/" on those, even after severa=
l reboots.
>=20

Oops responding to the whole list this time..

Um ouch your system appears to not be doing anything for like 300 secon=
ds but
sitting there.  Can you hook up a console and capture sysrq+w while tha=
ts going
on?  Also you are mounting with -o space_cache right?  Can I see your d=
mesg to
make sure it's doing what it's supposed to?  Thanks,

Josef
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