linux-kernel - Re: SUNRPC problem with 2.6.26 and beyond

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Date:	Wed, 22 Oct 2008 18:51:14 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Harry Edmon <harry@...os.washington.edu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: SUNRPC problem with 2.6.26 and beyond

On Wed, 2008-10-22 at 08:35 -0700, Harry Edmon wrote:
> I have a dual quad-core Xeon system running software 
> (http://www.unidata.ucar.edu/software/ldm) that relays and processes 
> weather data through RPC calls, keeping a queue of data in a memory 
> mapped file.  Up until 2.6.26 the system has run just fine (for example 
> 2.6.25.17).  But starting with 2.6.26 through 2.6.27.2 the system runs 
> into a problem after approximately 24 hours.  The symptom is that the 
> processing slows down to a crawl.  Using "top" I can see that the System 
> time is up over 90%, with almost no User and Wait time.  If I stop and 
> restart the software, most of the time it gets better - but sometimes it 
> takes a reboot to fix the problem.  I have an identical system that does 
> just processing and ingesting data from remote systems, and it does not 
> have this problem.  I have tried a number of different kernel 
> configurations, but they all show the same problem.
> 
> I suspect a problem with SUNRPC.  I notice that there were a large 
> number of SUNRPC patches in 2.6.26.  I am looking for suggestions on how 
> to pin down which patches are causing the problem.  Are there ways to 
> figure where in the  kernel the time is being spent?  I am will to work 
> on isolating the problem, but I need some suggestions on the best way to 
> do it given the large number of SUNRPC patches in 2.6.26 and the fact 
> that each experiment takes a day.

The kernel sunrpc interface is not exported to user land: the glibc code
uses its own, entirely separate implementation of sunrpc.

I cannot therefore see, how your application's RPC calls can be affected
by kernel sunrpc changes.

Cheers
  Trond

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