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XROOTD-L  May 2005

XROOTD-L May 2005

Subject:

Re: xrootd on (native) InfiniBand prototype

From:

Ulrich Schwickerath <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

2 May 2005 17:38:18 +0200Mon, 2 May 2005 17:38:18 +0200

Content-Type:

text/plain

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text/plain (104 lines)

Hi, Fabrizio,

thank's a lot for the fast answer!

>   Re-looking at your log I don't understand the problem. xrdcp is
> supposed to exit after having closed the file, so the connection is
> closed and the server notices this because there are no more bytes to
> read from the connection. Do I miss something?
Well, I'm using native InfiniBand. Basically, what you have is a pair of 
connected send and receive queue on both sides. If you want to send 
something, you post a send request on the sender side. The receiver, on the 
other hand, posts a receive request (containing the adress of the buffer 
where the data should go), and then  polls the receive queue. If some data 
has arrived, it will see a completion event. At that point the data has 
already arrived. The problem in this case is that if the sender does not send 
anything, the receiver will poll the receive queue until the time out is 
reached, and that is exactly what happens. My idea was to post a send request 
with no data attached, so that the receiver will not time out but see no data 
which would emulate the behavior that is expected.  
>
>   Anyway, the newer xrdcp, using the latest client, should avoid
> requesting data over the eof, that was one of the latest commits, but it
> implements a different schema for data transfers, which now are done
> both synchronously and asynchronously (i.e. in parallel, while the
> application "thinks"). The problem is that this stuff is in the head.
> Here it works, so if you are adventurous you can test it and report here
> if you have troubles.
I started with 20050413-0433, so I'll update to the new version that just came 
in :-)

Thank's a lot!
Ulrich

>
> Ulrich Schwickerath wrote:
> > Hi,
> >
> > I (finally) found a bit of time to work on a
> > port of Xrootd to (native) InfiniBand, and a
> > proof-of-concept version is now sort of working, meaning
> > that I can now transfer files with xrdcp. If possible, I would
> > like to show first results with this version at the ACAT05
> > conference in Berlin in about 3 weeks from now.
> > I have a few questions to you:
> >
> > 1/ what would be meaningful benchmark for xrootd ?
> >    For the moment, I'm only using point-to-point transfers
> >    (remote read to /dev/null, mainly) which is a bit boring ...
> >
> > 2/ Is there a ready-to-use test suite that can/should be used ?
> >
> > 3/ I still have one problem with xrdcp. For the client I have added
> > a few lines of code in the XrdClientPhyConnection.cc which
> > initializes my InfiniBand connection, and bypasses the recv/write
> > calls. Everything works fine until the end. The Server log looks
> > like this:
> > 050501 21:36:41 5282 schwicke.17140:12@iwrcgop027 XrootdProtocol: 0000
> > req=3003 dlen=0
> > 050501 21:36:41 5282 schwicke.17140:12@iwrcgop027 XrootdFile: closing
> > r /tmp/testfile.dat
> > 050501 21:36:41 5282 schwicke.17140:12@iwrcgop027 XrootdProtocol: 0000
> > close fh=0
> > 050501 21:36:41 5282 schwicke.17140:12@iwrcgop027 XrootdResponse: 0000
> > sending OK
> > 050501 21:36:44 5282 XrootdXeq: schwicke.17140:12@iwrcgop027 disc 0:04:24
> > (link read error)
> > 050501 21:36:44 5282 schwicke.17140:12@iwrcgop027 XrdPoll: sending poller
> > 0 detach for link 12
> > 050501 21:36:44 5282 XrdPoll: Poller 0 detached fd 12 entry 1 now at 1
> > 050501 21:36:44 5282 schwicke.17140:12@iwrcgop027 XrdPoll: FD 12 detached
> > from poller 0; num=0
> > For TCP/IP I see that the last recv request succeeds in the poll
> > command but ends with zero bytes of data, resulting in a ENOMSG return
> > code. For InfiniBand, this call simply times out, giving the above
> > link read error. A workaround would be to send a zero size message over
> > the InfiniBand link just before the connection is closed for good. I
> > tried to do that inside the XrdClientPhyConnection destructor, but that
> > one is never called in xrdcp. A side effect of this is that the resources
> > used by the InfiniBand connection need to be cleaned up and freed by the
> > driver resource tracking mechanisms. Where should this be done instead?
> >
> >
> > Thank's a lot in advance,
> > Ulrich

-- 
__________________________________________
Dr. Ulrich Schwickerath
Forschungszentrum Karlsruhe
GRID-Computing and e-Science
Institut for Scientific Computing (IWR)
P.O. Box 36 40
76021 Karlsruhe, Germany

Tel: +49(7247)82-8607
Fax: +49(7247)82-4972 

e-mail: [log in to unmask]
PGP DH/DSS Key: ID 0xCEB9826F
Fingerprint: 5537 8473 CD26 507E 8EE2  BAAF 98E2 FD16 CEB9 826F
__________________________________________


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