[openib-general] sysfs exposure of port counters useless?

[Hal Rosenstock]

On Tue, 2006-10-17 at 20:10, Michael Newton wrote:
> On Tue, 17 Oct 2006, Hal Rosenstock wrote:
> > On Tue, 2006-10-17 at 09:55, Rimmer, Todd wrote:
> > > > From: Michael Newton
> > > > Sent: Tuesday, October 17, 2006 3:02 AM
> > > > To: openib-general at openib.org
> > > > Subject: [openib-general] sysfs exposure of port counters useless?
> > > >
> > > >
> > > > These are 32 bit counters. The rcv/xmit_data counters count 32-bit
> > > > blocks. Also, these counts do not wrap: they peg at all 1s.
> > > > At infiniband speeds, these counts can peg out very quickly indeed,
> > > > to the point they can really only be of use if they can be reset each
> > > time
> > > > there read. Now if anyone who wants to use them has to go the CLI to
> > > reset
> > > > them, and theres little point in reading them without reset, why would
> > > > anyone read them via sysfs? so why have them?
> > > >
> > >
> > > We have found that while your comment is true for the data movement
> > > counters, the error counters should not peg quickly, hence it is valid
> 
> its true i overstated the case just a little;) .. yes error counters
> should be fine and its mainly the data counters that are problematic
> (tho now im not sure i havent seen the packet counters freeze when the
> data ones peg out)..
> 
> > > to read them without resetting.  However it is also useful to have an
> > > ability to reset them.  Of course if there are other CLI commands which
> > > do this easily, the sysfs info is of less value.
> >
> > There are diag tools for this.
> 
> thats where we started.. 

Guess I missed that.

> the point im making is that exposing the data
> counters in sysfs is of little use, because if you have to go to other
> tools to reset, why wouldnt you use them to read as well?

You can. They support this.

> i was looking at exposing infiniband stats via PCP
> (http://oss.sgi.com/projects/pcp/). This would be useful for folk doing IB
> performance testing. Its very easy to just feed in the sysfs values..
> unfortunately they turn out to be of little value. Life would be so much
> easier if there were 64 bit counters available. Instead I will probably
> need to have an additional daemon to construct them.

Depends on what you mean by available. They are defined in the IB spec
(PortCountersExtended) but are optional and not available in all PMAs.

-- Hal