zfs discuss - Nov 2008 - RC1 Zfs writes a lot slower when running X

Hi,

I have OpenSolaris on an Amd64 Asus-A8NE with 2gig of Rams and 4x320 gig sata
drives in raidz1.

With dd, I can write at quasi disk maximum speed of 80meg each for a total of
250meg/s if I have no Xsession at all (only console tty).

But as soon as I have an Xsession running, the write speed drops to about
120MB/s.
Its even worse if I have a VBoxHeadless running with an idle win2k3 inside. It
drops to 30 MB/s.

The CPU is at 0% in both cases and nothing is using the array either. I tried to
investigate with DTrace without success...

Anyone have a clue of what could be going on?

Thanks

Zerk
-- 
This message posted from opensolaris.org

On Fri, Nov 21, 2008 at 11:33 PM, zerk <zerk666 at gmail.com> wrote:
> Hi,
>
> I have OpenSolaris on an Amd64 Asus-A8NE with 2gig of Rams and 4x320 gig
> sata drives in raidz1.
>
> With dd, I can write at quasi disk maximum speed of 80meg each for a total
> of 250meg/s if I have no Xsession at all (only console tty).
>
> But as soon as I have an Xsession running, the write speed drops to about
> 120MB/s.
> Its even worse if I have a VBoxHeadless running with an idle win2k3 inside.
> It drops to 30 MB/s.
>
> The CPU is at 0% in both cases and nothing is using the array either. I
> tried to investigate with DTrace without success...
>
> Anyone have a clue of what could be going on?
>
> Thanks
>
> Zerk
> --
>
Ya, you''re using gobs of ram that was normally being used by zfs for
caching.  I would venture to guess if you stuck another 2GB ram in there
you''d see far less of a *hit* from X or a VM.

--Tim
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Hi,

thanks for the reply

I though that was that too, so I wrote a C program that allocated 1 gig of ram
doing nothing with it. So the system was left with only 1 gig for ZFS and I saw
absolutely no performance hit.

I tried the same thing for the CPU by doing a loop and taking 100% on one of the
2 core I have. Same thing... no hit at all.

I think it have something to do with system calls, kernel or some like that but
I don''t know enough on that to be able to diagnose such a problem...

The video card I have in there is an old Matrox G200 PCI because this is all I
got left and because I didn''t need anything better than that on a
server. I disabled the console X server and I only connect via Xvnc server so I
would be really surprise if Xvnc is doing something with that card but we never
know...

Thanks

Zerk
-- 
This message posted from opensolaris.org

>Hi,
>
>thanks for the reply
>
>I though that was that too, so I wrote a C program that allocated 1 gig of
>ram doing nothing with it. So the system was left with only 1 gig for ZFS
>and I saw absolutely no performance hit.
Lock it in memory and then try again; if you allocate the memory but you
don''t use it, you only have a swap reservation, nothing more.

But if you allocate and then run mlockall(MCL_CURRENT), you take 1GB
of the table.

Casper

Great it worker,

mlockall returned -1 probably because the system wasn''t able to
allocate blocks of 512M contiguously... but using memset for each blocks
commited the memory and I saw the same zfs perf problem as with X & Vbox.

Thanks a lot for the hint :)

Now I guess i''ll have to buy more RAM :)

zerk
-- 
This message posted from opensolaris.org

On Fri, 21 Nov 2008, zerk wrote:
> I have OpenSolaris on an Amd64 Asus-A8NE with 2gig of Rams and 4x320 gig
sata drives in raidz1.
>
> With dd, I can write at quasi disk maximum speed of 80meg each for a total
of 250meg/s if I have no Xsession at all (only console tty).
>
> But as soon as I have an Xsession running, the write speed drops to 
> about 120MB/s. Its even worse if I have a VBoxHeadless running with 
> an idle win2k3 inside. It drops to 30 MB/s.
I believe that the OpenSolaris kernel is now extended such that it 
reports file change events to Gnome for files in the user''s home 
directory.  When Gnome hears about a change, then it goes and reads 
the file so that searching is fast and there is a nice per-generated 
thumbnail.  This means that there is more than simple memory 
consumption going on.

Try writing into the same pool but outside of your home directory and 
see if the I/O rate improves.  If it does, then go complain on the 
Desktop list.  I already complained in advance on the Desktop list but 
where was little response (as usual) so I have since unsubscribed.

Bob
=====================================Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

>Great it worker,
>
>mlockall returned -1 probably because the system wasn''t able to
allocate blocks of 512M contiguous
ly... but using memset for each blocks commited the memory and I saw the same
zfs perf problem as w
ith X & Vbox.

You need to be have the proper privilege. Ordinary users cannot
lock memory.

Casper