From: Trond Myklebust <trond.myklebust@fys.uio.no>
Subject: RE: [PATCH] 1/3 - RPC metrics support
Date: Wed, 31 Mar 2004 12:19:09 -0500
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <1080753549.4194.60.camel@lade.trondhjem.org>
References: <482A3FA0050D21419C269D13989C61130435DE34@lavender-fe.eng.netapp.com>
Mime-Version: 1.0
Content-Type: text/plain
Cc: Patrick Mochel <mochel@digitalimplant.org>, nfs@lists.sourceforge.net
To: Charles Lever <Charles.Lever@netapp.com>
In-Reply-To: <482A3FA0050D21419C269D13989C61130435DE34@lavender-fe.eng.netapp.com>
Errors-To: nfs-admin@lists.sourceforge.net

On Wed, 2004-03-31 at 11:57, Lever, Charles wrote:
> > My experience with gettimeofday() was that it slows down and 
> > eventually hangs the machine when you use it inside bottom 
> > halves. That's why I had to revert to using 'jiffies' 
> > instead. While I agree that precision may be important, a 
> > measurement that so impacts on what it is measuring is not 
> > particularly useful either...
> 
> using jiffies makes these measurements useless for anything
> faster than a millisecond (or 10 milliseconds on current
> x86), which is most everything on 100Mb or faster, these
> days.  isn't there some other solution?

In 2.6. jiffies have 1 ms resolution, not 10 on x86. There may be some
alternative generic timing solution in Linux that does better than that,
and that can work within bottom halves without side-effects but I'm not
aware of such a solution.

You can of course use do_gettimeofday() for the non bh-safe parts if you
want to, but using it inside things like *data_ready() etc. was clearly
unacceptable.

The only generic solution I see is therefore to use statistics...

Cheers,
  Trond


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