Re: redhat 2.4.18-5 client huge slowdown

Re: redhat 2.4.18-5 client huge slowdown

[Rex Dieter]

On Thursday 11 July 2002 2:02 pm, Trond Myklebust wrote:
> >>>>> " " =3D=3D Rex Dieter <rdieter@math.unl.edu> writes:
>      > Yes, I've also experienced a huge nfs client slowdown (~50k/sec
>      > writes) on 'sync' nfs mounts with the 2.4.18-5 kernel... See me
>      > bugzilla report:
>      > http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=3D67199 and =
a
>      > similar report as well:
>      > http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=3D67461
>
>      > The only way I found to get any sort of respectable performance
>      > out of 2.4.18-5 was to mount 'async'. *ack*
>
> For 2.4.18-5 RedHat appears to have decided to set the default r/wsize
> to 4k.=20

For me, the r/wsize made no significant difference as long as the 'sync'=20
option was used.  Write speeds consistantly stayed ~50k/sec.

-- Rex



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Re: [PATCH] 2.4.19-rc1/2.5.25 provide dummy fsync() routine for directories on NFS mounts

[Rex Dieter]

Trond Myklebust <trond.myklebust@fys.uio.no> wrote:

> >>>>> " " =3D=3D Matthias Andree <ma@dt.e-technik.uni-dortmund.de> writ=
es:
>      > What if the NFS stuff is not mounted with sync or explicitly
>      > mounted async? Will an nfsd still do synchronous writes to
>      > directories?

> Of course. It is not possible for the NFS client to switch this
> behaviour off, since it is part of the server side specifications in
> the protocol.
> The only thing that can screw you up is if you use the 'async' option
> in /etc/exports on the server.

How is specifying 'async' in /etc/exports on the NFS server different tha=
n a=20
NFS client explicitly mounting async?

-- Rex


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Re: [PATCH] 2.4.19-rc1/2.5.25 provide dummy fsync() routine for directories on NFS mounts

[Tom McNeal]

Rex Dieter wrote:
> 
> Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
> 
> > >>>>> " " == Matthias Andree <ma@dt.e-technik.uni-dortmund.de> writes:
> >      > What if the NFS stuff is not mounted with sync or explicitly
> >      > mounted async? Will an nfsd still do synchronous writes to
> >      > directories?
> 
> > Of course. It is not possible for the NFS client to switch this
> > behaviour off, since it is part of the server side specifications in
> > the protocol.
> > The only thing that can screw you up is if you use the 'async' option
> > in /etc/exports on the server.
> 
> How is specifying 'async' in /etc/exports on the NFS server different than a
> NFS client explicitly mounting async?
> 
> -- Rex


The /etc/exports async option allows the server to tell the client
that it has indeed written data/metadata to the disk, regardless
of what has actually happened.

So, the client sync/async affects *when* the client writes to the
server, and the server sync/async affects *how* (OK, and *when*) the 
server replies to the client.  

Regards -

Tom

--
------------------------------------------------------------
Tom McNeal       trmcneal@attbi.com     (650)906-0761 (cell) 
------------------------------------------------------------


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Re: redhat 2.4.18-5 client huge slowdown

[Rex Dieter]

Rex Dieter <rdieter@math.unl.edu> wrote:
> Raphael Clifford wrote:
> > I was wondering if everyone else is experiencing huge nfs write
> > slowdowns using redhat kernel 2.4.18-5 (as opposed to 2.4.18-4).  I a=
m
>
> Yes, I've also experienced a huge nfs client slowdown (~50k/sec writes)=
 on
> 'sync' nfs mounts with the 2.4.18-5 kernel... See me bugzilla report:
> http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=3D67199
=2E..

Here's some interesting data (on switched fast ethernet) to chew on (usin=
g=20
Redhat's 2.4.18-5 kernel on both server and client):
Server(1)  Client(2)  Speed=20
async      async     ~8.5MB/sec=20
async      sync      ~6.5MB/sec=20
sync       async     ~350K/sec=20
sync       sync      ~50k/sec=20
=20
(1) using the 'async/sync' option in /etc/exports
(2) using the 'async/sync' option when mounting, ie, mount -t nfs -o sync=
 ...

Is this really the kind of performance I should expect to get? (I hope no=
t)

-- Rex


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Re: redhat 2.4.18-5 client huge slowdown

[Trond Myklebust]

>>>>> " " == Rex Dieter <rdieter@math.unl.edu> writes:

     > Here's some interesting data (on switched fast ethernet) to
     > chew on (using Redhat's 2.4.18-5 kernel on both server and
     > client): Server(1) Client(2) Speed async async ~8.5MB/sec async
     > sync ~6.5MB/sec sync async ~350K/sec sync sync ~50k/sec
 
If you switch off write caching using the '-o sync' mount option then
of course you will see a dramatic slowdown. Where's the beef?

Cheers,
  Trond


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redhat 2.4.18-5 client huge slowdown

[Raphael Clifford]

I was wondering if everyone else is experiencing huge nfs write 
slowdowns using redhat kernel 2.4.18-5 (as opposed to 2.4.18-4).  I am 
using a Sun Solaris machine as the server and following mount options.

rw,rsize=32768,wsize=32768,nfsvers=3,proto=tcp

I understand that both 2.4.18-4 and 2.4.18-5 default to 'sync' but as 
the slow down is between those versions so that shouldn't make any 
difference.  I also understand that there were a lot of nfs client 
"fixes" in 2.4.18-5 so I assume they have caused this problem.

The linux machine is a dual 500 MHz if that makes any difference.

Cheers,
Raphael



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Re: redhat 2.4.18-5 client huge slowdown

[Tom McNeal]

Raphael Clifford wrote:

> I was wondering if everyone else is experiencing huge nfs write 
> slowdowns using redhat kernel 2.4.18-5 (as opposed to 2.4.18-4).  I am 
> using a Sun Solaris machine as the server and following mount options.
> 
> rw,rsize=32768,wsize=32768,nfsvers=3,proto=tcp
> 
> I understand that both 2.4.18-4 and 2.4.18-5 default to 'sync' but as 
> the slow down is between those versions so that shouldn't make any 
> difference.  I also understand that there were a lot of nfs client 
> "fixes" in 2.4.18-5 so I assume they have caused this problem.
> 
> The linux machine is a dual 500 MHz if that makes any difference.
> 
> Cheers,
> Raphael
> 


The sync/async default is determined at the server, not the client,
and Solaris defaults to sync, as does almost everyone else.

Also, the default is determined in the utilities, not in the kernel,
which is why Linux servers currently default to async.  They will
default to sync when using the latest, unreleased export utilites;
They will be released "very soon" as version 1.0.1.

Regards -

Tom
--
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Tom McNeal           trmcneal@attbi.com           (650)906-0761 (cell)
----------------------------------------------------------------------



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Re: redhat 2.4.18-5 client huge slowdown

[Yusuf Goolamabbas]

Can you see if reducing rsize,wsize to 8192 seems to help

This bugzilla entry is referenced by the 2.4.18-5 kernel release note

http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=64984

Add your observations to it if it makes a difference

> I was wondering if everyone else is experiencing huge nfs write 
> slowdowns using redhat kernel 2.4.18-5 (as opposed to 2.4.18-4).  I am 
> using a Sun Solaris machine as the server and following mount options.
> 
> rw,rsize=32768,wsize=32768,nfsvers=3,proto=tcp
> 
> I understand that both 2.4.18-4 and 2.4.18-5 default to 'sync' but as 
> the slow down is between those versions so that shouldn't make any 
> difference.  I also understand that there were a lot of nfs client 
> "fixes" in 2.4.18-5 so I assume they have caused this problem.
> 
> The linux machine is a dual 500 MHz if that makes any difference.
> 
> Cheers,
> Raphael


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