[ENBD] Doubled requests

[Arne Wiebalck]

On Tue, 13 Jan 2004, Peter T. Breuer wrote:

> > I don't think it's an accounting error. I am quite good at counting ;-)
>
> OK.

I used my resource directly (without enbd) and could write more than
100,000,000 requests without seing a request being delivered multiple
times. The number of requests reported was exactly the number I expected.

Checked again with enbd (show_errs=1, increased req_timeo to 30 instead
of 5), but after 102,400 requests the device reported 102,401.

I'll investigate further. Let's see what I can find out ...

[snip]

> Anyway, the server ought to shout if it notices a double write.
>
> Maybe the cache is too small to notice?

Is the driver or the enbd-client (or can be both) the source of a
retransmission?

> If you see no rollbacks in the client, the client is not
> retransmitting.

Hmmm.

> I also know of no way the server could redo a request on its own.

More hmmmm.

I'll add some code to my device to notify me if it sees requests to the
same block. Maybe we can conclude something if we see the request series
to be

  .. 22 23 24 25 25 26 27 ...
              ^^^^^

or

  .. 22 23 24 25 26 27 28 ... 110 25 111 112 113 ...
              ^^                  ^^

since the first case should be handled by the cache, while it may be too
small for the second.

 arne



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 Arne Wiebalck                        Kirchhoff Institute for Physics
                                           Technical Computer Science
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