[gentoo-dev] Gentoo kernel and XFS

[gentoo-dev] Gentoo kernel and XFS

[Emiel Kollof]

Hi list,

I've been running Gentoo 1.2 for some time now, and it's pretty nifty, but I 
have a nit to pick.

I use XFS. The Gentoo kernel has the preemptible kernel patch. Somehow, those 
two don't play nice together. It seems that the xfs code throws away stuff 
they lock a bit carelessly, and it's wreaking havoc with the preempt-kernel 
patch.

Note that there is no stability and/or data loss, but the preempt patch  
cannot preempt because of this, and other than not doing preemption, it's 
filling up my logs with silly messages. I can patch the kernel not to show 
the crappy messages, but that would defeat the purpose of having a 
preemptible kernel, because it cannot preempt anything anyway.

I know this is being worked on, and the newest CVS version of the XFS drivers 
have solved this problem. The XFS developers that the CVS version is very 
stable, so I'm asking if it's possible to put the cvs version of the xfs 
stuff in the gentoo-enhanced kernel.

If this is not possible, well, I'd like to know what patches are incorporated 
into this kernel so I can apply it my damn self :)

Cheers,
Emiel

Re: [gentoo-dev] Gentoo kernel and XFS

[Brandon Low]

Use the latest xfs-sources.  Has xfs and other useful things, but none of 
the performance patches that mess things up...

Or quit using xfs, and use my personal fav. reiserfs and then use 
gentoo-sources-2.4.19-r9

On Wed, 09/11/02 at 04:41:07 +0200, Emiel Kollof wrote:
> Hi list,
> 
> I've been running Gentoo 1.2 for some time now, and it's pretty nifty, but I 
> have a nit to pick.
> 
> I use XFS. The Gentoo kernel has the preemptible kernel patch. Somehow, those 
> two don't play nice together. It seems that the xfs code throws away stuff 
> they lock a bit carelessly, and it's wreaking havoc with the preempt-kernel 
> patch.
> 
> Note that there is no stability and/or data loss, but the preempt patch  
> cannot preempt because of this, and other than not doing preemption, it's 
> filling up my logs with silly messages. I can patch the kernel not to show 
> the crappy messages, but that would defeat the purpose of having a 
> preemptible kernel, because it cannot preempt anything anyway.
> 
> I know this is being worked on, and the newest CVS version of the XFS drivers 
> have solved this problem. The XFS developers that the CVS version is very 
> stable, so I'm asking if it's possible to put the cvs version of the xfs 
> stuff in the gentoo-enhanced kernel.
> 
> If this is not possible, well, I'd like to know what patches are incorporated 
> into this kernel so I can apply it my damn self :)
> 
> Cheers,
> Emiel
> _______________________________________________
> gentoo-dev mailing list
> gentoo-dev@gentoo.org
> http://lists.gentoo.org/mailman/listinfo/gentoo-dev

Re: [gentoo-dev] Gentoo kernel and XFS

[Emiel Kollof]

On Wednesday 11 September 2002 05:23, Brandon Low wrote:

> Use the latest xfs-sources.  Has xfs and other useful things, but none of
> the performance patches that mess things up...

It's not messing anything up. It's just not doing anything, which is a bit of 
a waste. My idea was to use the latest xfs sources, but if I knew which 
patches were in the gentoo-enhanced kernel, I could chuck them in there as 
well. Robert Love, the creator of the preempt patch says that preemt-kernel 
and XFS do play nice together, as long as XFS keeps it's act clean and neatly 
disposes of it's locks instead of just trashing them when it doesn't need it 
anymore :) 

XFS is very stable, production use stable even. It passed all my file 
corruption tests with flying colors, and it can deal with the size of files I 
usually juggle around, which are big raw unedited full motion video files 
which easily take up multiple gigabytes. 

Oh, and those patches are useful to me, since I need low latency for stuff 
like video editing (which somewhat needs real-time preformance and low 
latency). I can't just drop them, my video editing tools would turn out crap. 
I got some good latency times on an ext3 fs and the already present 
performance patches (latency times around a few milliseconds, which is just 
about doable), but the filesystem sucked. So I switched to xfs. Great 
filesystem, fits my needs perfectly, but now the preempt-kernel isn't 
preempting and I'm seeing the latency times skyrocket because some procs are 
seizing cycles when they shouldn't and things start to skip horridly. Urgh. 

> Or quit using xfs, and use my personal fav. reiserfs and then use
> gentoo-sources-2.4.19-r9

Quit using XFS? Not an option. I'm not too fond of backing all this crap up 
It's a lot, hence the XFS. I'm talking hundreds of GB's here. Some files grow 
generously larger 2 GB as well. Sucks to be me huh? 

Oh, and I don't like reiser. It's great for small files, but I don't have many 
of those, other than the usual. I did some tests with a fairly recent 
reiserfs once, and it showed me that it sucked for the size of databases and 
raw movie files I usually muck with. It's not a bad fs, but the wrong tool 
for my job/hobbies/whatever.

But I'm digressing: So far, the only two things I could discern wrt 
performance patches are the O(1) scheduler and the preemptible kernel. Is 
there any more you folks propped in there, other than those two?

Cheers,
Emiel

Re: [gentoo-dev] Gentoo kernel and XFS

[Christian Skarby]

> If this is not possible, well, I'd like to know what patches are
> incorporated  into this kernel so I can apply it my damn self :)

/usr/portage/sys-kernel/gentoo-sources/gentoo-sources-2.4.19-r9.ebuild

I think one can figure it out from this ebuild. The ebuild is using a
vanilla kernel source and applies some patches on that. The patches are
stored in  http://gentoo.lostlogicx.com/patches-${KV}.tar.bz2 i.e. 
http://gentoo.lostlogicx.com/patches-2.4.19-gentoo-r9.tar.bz2

Not sure if this is to any help, but I hope it is :)


Christian

Re: [gentoo-dev] Gentoo kernel and XFS

[Jean-Michel Smith]

On Wednesday 11 September 2002 02:00 am, Emiel Kollof wrote:

> XFS is very stable, production use stable even. It passed all my file
> corruption tests with flying colors, and it can deal with the size of files
> I usually juggle around, which are big raw unedited full motion video files
> which easily take up multiple gigabytes.

Exactly.  I use it for the same reason, and as one who has tried several 
filesystems, including reiser, ext3, and others, XFS is by far the most 
stable I've come across under Linux.

> Oh, and those patches are useful to me, since I need low latency for stuff
> like video editing (which somewhat needs real-time preformance and low
> latency). I can't just drop them, my video editing tools would turn out
> crap. I got some good latency times on an ext3 fs and the already present
> performance patches (latency times around a few milliseconds, which is just
> about doable), but the filesystem sucked. So I switched to xfs. Great
> filesystem, fits my needs perfectly, but now the preempt-kernel isn't
> preempting and I'm seeing the latency times skyrocket because some procs
> are seizing cycles when they shouldn't and things start to skip horridly.
> Urgh.

Don't use preempt with XFS.  Stick with low latency only.  Regardless of what 
the preempt author says, under gentoo-sources-2.4.19-r7 I have personally 
witnessed preempt NOT playing nicely with XFS.  In fact, for whatever reason, 
my performance improved when I took preempt out but left low latency in 
(probably because preempt was clobbering XFS access and writes in some way).

> > Or quit using xfs, and use my personal fav. reiserfs and then use
> > gentoo-sources-2.4.19-r9
>
> Quit using XFS? Not an option. I'm not too fond of backing all this crap up
> It's a lot, hence the XFS. I'm talking hundreds of GB's here. Some files
> grow generously larger 2 GB as well. Sucks to be me huh?

Like you, I use and deploy XFS quite widely, and given past experiences I've 
had personally with reiserfs cheerfully dropping entire directory trees into 
the bit bucket under what can only be described as mysterious circumstances 
I, like you, am disinclined to change (regardless of the assurances that 'it 
won't happen again').  I agree with you, XFS is a production ready 
filesystem, while the other journaled filesystems are at best a crapshoot.  
It sucks XFS is not a part of the kernel, and the patch is so intrusive that 
preempt breaks, but it is IMHO worth it.

Again, I use gentoo-sources-r7, which includes XFS support.  I use low 
latency, BUT I TURN OFF PREEMPT.  That is important.  Preempt doesn't play 
nice with XFS (the only time I was ever able to corrupt an XFS filesystem was 
while beating it up under a kernel with preempt enabled).  I have had very 
good results with the low latency stuff.

Jean.

PS - What video editing software do you use?

Re: [gentoo-dev] Gentoo kernel and XFS

[Seth Mos]

At 07:06 11-9-2002 -0500, Jean-Michel Smith wrote:
>On Wednesday 11 September 2002 02:00 am, Emiel Kollof wrote:
>
> > XFS is very stable, production use stable even. It passed all my file
> > corruption tests with flying colors, and it can deal with the size of files
> > I usually juggle around, which are big raw unedited full motion video files
> > which easily take up multiple gigabytes.
>
>Exactly.  I use it for the same reason, and as one who has tried several
>filesystems, including reiser, ext3, and others, XFS is by far the most
>stable I've come across under Linux.

AFAIK the preempt patch is not integrated into the mainline kernel. This 
alone makes the user base that test and notice these sort of things a _lot_ 
smaller.

The XFS developers only test against the mainline vanilla 2.4 or 2.5. Other 
people will (and do!) test the cooperation with other patches. The 
developer team at SGI that works on XFS is very small and the priority is 
the integration with the mainstream vanilla tree. Testing with other 
patches is down the priority list. They are willing to accept patches but 
they don't have the time to investigate it them self.

I personally have not tested either the preempt patches, the low latency 
patches or the new scheduler and have come accross very few problems with 
XFS filesystems in general. So far I have never lost a XFS filesystem yet 
(not by screwing it up myself that is) due to a failure in XFS itself.

Things to not do (from almost 2 years mailinglist membership):
- Use overclocked hardware.
- Use a bad compiler (see faq).
- Overwrite the superblock with lilo or GRUB.
- Running repair tools without swap!
- Not testing it in your own environment.

I did have crashes in the distant past, filesystem corruption during 
poweroff and such in the 2.4.0-test days. And to be honest that wasn't a 
feature that was only available on XFS filessytems ;)

Cheers

--
Seth
It might just be your lucky day, if you only knew.

Re: [gentoo-dev] Gentoo kernel and XFS

[Emiel Kollof]

On Wednesday 11 September 2002 14:06, Jean-Michel Smith wrote:
> On Wednesday 11 September 2002 02:00 am, Emiel Kollof wrote:

[snip]

> Again, I use gentoo-sources-r7, which includes XFS support.  I use low
> latency, BUT I TURN OFF PREEMPT.  That is important.  Preempt doesn't play
> nice with XFS (the only time I was ever able to corrupt an XFS filesystem
> was while beating it up under a kernel with preempt enabled).  I have had
> very good results with the low latency stuff.

Ah right... I'll give that a go. Thanks for the info.

> PS - What video editing software do you use?

Some proprietary homegrown stuff some colleagues and I wrote that originally 
ran on IRIX but which I ported over to Linux. I can't live without it, but 
it's a shame I can't opensource it. It has lots of licensed code I can't open 
up and without that it would be quite useless. :(

Cheers,
Emiel

Re: [gentoo-dev] Gentoo kernel and XFS

[Benjamin Podszun]

On Wed, 2002-09-11 at 14:06, Jean-Michel Smith wrote:
> It sucks XFS is not a part of the kernel, and the patch is so intrusive that 
> preempt breaks, but it is IMHO worth it.

Wait a little. Afaik XFS _is_ part of the current 2.5-series kernel
now..
Let's hope there will be a stable release soon. ;-)

Ben