[OpenAFS] Re: Performance problems seem to be coming back

Jeffrey Altman jaltman@your-file-system.com
Mon, 12 Sep 2011 12:12:35 -0400

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On 9/12/2011 11:31 AM, Dale Pontius wrote:
> Maybe I'm missing what rxdebug really does, but I think it sounds just
> about perfect.  I presume that the OpenAFS clients and servers have
> packet queues for moving data, and rxdebug just drops packets into thos=
> queues like any other part of afs.  If the other parts of afs queue are=

> in "distress" for whatever reason, all of the other packets in that
> queue will share in the distress, including my rxdebug requests.  In
> this case, that's what I want - to be told about "distress" between the=

> server and me, and for the first approximation I'm not too concerned
> about the reason, just that it exists.
> The specific reason for the distress is the next layer of the onion, an=
> the difference between (my interpretation of) the rxping and a UDP ping=

> that doesn't go through the afs server could be part of that.
> Dale Pontius

An ICMP ping (not UDP) is processed by the IP stack of the receiving
machine and does not get seen by any applications.

A UDP ping such as the "echo" service provides information about the
delivery of UDP packets and response after processing by an application
on the machine.

An rxdebug -ver (version query) is similar to a UDP "echo" service
request in that is it processed by an application.  The difference
between an rx version query and an AFS GetTime RPC is that the rx layer
will reply immediately to a version query and will not queue an RPC to
be processed by a file server worker thread.

The probes performed by the AFS cache manager are AFS RPCs which require
processing by the File Server or Volume Location server worker threads.
 As such, the cache manager will mark down a server that is not
responding to RPCs even though the Rx layer is happily responding to
version queries.

Jeffrey Altman

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