Re: NFS client (10x) performance regression 2.6.14.7 -> 2.6.15

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Fri, 2006-03-31 at 11:48 +0200, Jakob Oestergaard wrote:
> Hi guys,
> 
> I just found out... Installed 2.6.16.1 (32-bit) on a spanking new dual
> opteron 275 (dual-core) machine, and saw that my link jobs were taking
> ages.
> 
> I narrowed it down a bit - these are the kernels I have tested:
> 2.6.13.5:  Good
> 2.6.14.7:  Good
> 2.6.15:    Poor
> 2.6.15.7:  Poor
> 2.6.16.1:  Poor
> 
> Sequential NFS I/O is good on all kernels. Only "ld" shows the problem.
> 
> On 2.6.14.7, I can run a large link job creating a 60 MB executable in
> 15.6 seconds wall-clock time.
> 
> On 2.6.15, the same link job takes 2 minutes 28 seconds.
> 
> This is almost 10 *times* longer.
> 
> Testing with tiobench, I can see no notable difference between the
> kernels (!)   It seems that this is very specific to ld.  I am using GNU
> ld version 2.15.
> 
> The NFS client mounts the working directory using NFS v3 over UDP with
> default (32k) rsize/wsize.
> 
> Since this machine is not in production yet, I can experiment with
> kernel patches on it - I would like to try and narrow this down even
> further - any suggestions as to which patches to exclude/include will be
> greatly appreciated.

Some nfsstat output comparing the good and bad cases would help.

Cheers,
  Trond