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

[Sergei Trofimovich <slyich@gmail.com>]

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On Sat, 21 Apr 2012 22:54:41 +0200
Ahmet Inan <ainan@mathematik.uni-freiburg.de> wrote:

> On Fri, Apr 13, 2012 at 3:47 PM, Josef Bacik <josef@redhat.com> wrote:
> > On Fri, Apr 13, 2012 at 02:26:19PM +0200, Ahmet Inan wrote:
> >> On Fri, Apr 13, 2012 at 1:22 PM, Ahmet Inan
> >> <ainan@mathematik.uni-freiburg.de> wrote:
> >> > On Fri, Apr 13, 2012 at 8:49 AM, cwillu <cwillu@cwillu.com> wrote:
> >> >>> dmesg and fstab attached as requested.
> >> >>
> >> >> Need dmesg after you've hit alt-sysrq-w a couple times during the slow period.
> >> >
> >> > here.
> >> >
> >> > i guess i should also increase dmesg history size next time.
> >> > other than the slow boot, everything seems normal after 10-20minutes.
> >> >
> >> > fyi: the space_cache option is not really helping with those
> >> > twenty computers. the one thing i observed is, that sometimes
> >> > they reboot fast and only to reboot slow again after that.
> >>
> >> sorry for spaming the list with my dmesg files,
> >> please tell me, how i could do better.
> >>
> >> here a more complete dmesg.
> >
> > Hrm so you are getting blocked task warnings just trying to mount the
> > filesystem, so either your disk is really really really slow or there's
> > something bigger going on.  Let me think about this some and I'll get back to
> > you.
> 
> Josef, i finally found out something:
> 
> btrfs in kernel => fast boot
> btrfs as module => very slow boot
> 
> and here see the results:
> http://aam.mathematik.uni-freiburg.de/IAM/homepages/ainan/bootchart_btrfs_in_kernel.png
> 
> this is much, much better!
> 
> I dont understand why btrfs as a module performs that bad on rotating disk.
> On SSD i had no issues and also i never used space_cache before.

There is a suspiction that putting space_cache (or anything else) to fstab for rootfs
does not get applied due to a bug:

    http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg16039.html

Do all of your affected computers run 3.4.0-rc kernels?

-- 

  Sergei

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