openssh unix dev - Feb 2002 - [Bug 105] scp protocol 2 over a hippi interface takes 6 times longer

http://bugzilla.mindrot.org/show_bug.cgi?id=105

markus at openbsd.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED



------- Additional Comments From markus at openbsd.org  2002-02-07 06:54 -------
could you please try this without scp? e.g.

cat file | ssh -1 -c 3des 'cat > f'
cat file | ssh -2 -c 3des-cbc 'cat > f2'

thanks.



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------- Additional Comments From pas50 at cam.ac.uk  2002-02-07 20:51 -------
time `cat lapack.ibm.tar.gz | ssh -1 -c 3des hodgkin 'cat > f' `
10.6u 0.6s 0:24 45% 954+790k 0+0io 0pf+0w

time `cat lapack.ibm.tar.gz | ssh -2 -c 3des-cbc hodgkin  'cat > f2'
`
8.9u 0.7s 2:40 6% 929+631k 0+0io 0pf+0w

My colleague has done some investigating and has found something up with select.

"I have added some diagnostics to
packet.c and clientloop.c.  It is clear that the slow select calls
are not working properly - in particular, they are returning after
about 0.2 seconds WITHOUT having set a descriptor.  Subsequent
calls work.  It seems to be input from the connexion that is the
problem.

I suspect a failure to communicate from the HiPPI driver, which
then triggers a timeout."



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------- Additional Comments From pas50 at cam.ac.uk  2002-02-08 04:31 -------
This is a problem with the nagle algoithm and a delayed ack timer
http://www.rs6000.ibm.com/support/sp/perf/nagle21.html

describes the problem over an IBM switch which again is a network with a large
MTU. (The same problem accors using scp over this type of network.)

The best solution to this is to be able to have larger packets for networks that
can support them. 




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------- Additional Comments From pas50 at cam.ac.uk  2002-02-09 02:09 -------
Changing channels.h
#define CHAN_SES_WINDOW_DEFAULT (32*1024)
#define CHAN_TCP_WINDOW_DEFAULT (32*1024)
to
#define CHAN_SES_WINDOW_DEFAULT (256*1024)
#define CHAN_TCP_WINDOW_DEFAULT (256*1024)
Fixes the buffer problem. 
Scp is still 8 times slower than rcp. The time isn't used in CPU so there is
still scope for improvement.



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------- Additional Comments From pas50 at cam.ac.uk  2002-02-11 21:30 -------
time `cat lapack.ibm.tar.gz | ssh -1 -c 3des hodgkin 'cat > f' `
9.2u 0.7s 0:22 44% 887+761k 0+0io 0pf+0w
time `cat lapack.ibm.tar.gz | ssh -2 -c 3des-cbc hodgkin  'cat > f2'
`
8.7u 0.7s 0:22 41% 888+630k 0+0io 0pf+0w
time `cat lapack.ibm.tar.gz | rsh  hodgkin  'cat > f2' `
0.0u 0.0s 0:01 2% 77+214k 0+0io 0pf+0w



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------- Additional Comments From markus at openbsd.org  2002-02-12 03:30 -------
hm, i think
#define CHAN_SES_WINDOW_DEFAULT (256*1024)
#define CHAN_TCP_WINDOW_DEFAULT (256*1024)
generates packets > 32k, but i have to cross check.
does 64*1024 help.

what about using a faster cipher in your tests? :)
e.g blowfish?



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------- Additional Comments From pas50 at cam.ac.uk  2002-02-12 04:08 -------
time `cat lapack.ibm.tar.gz | ssh -2 -c blowfish-cbc hodgkin  'cat >
f2' `
2.6u 0.6s 0:06 46% 736+532k 0+0io 0pf+0w
Yep much faster but still not more than half the time in the cpu.

Yep packet size is a function of these values
#define CHAN_SES_PACKET_DEFAULT (CHAN_SES_WINDOW_DEFAULT/2)
#define CHAN_TCP_PACKET_DEFAULT (CHAN_TCP_WINDOW_DEFAULT/2)

The networks I saw the problem on hippi and IBM sp switch both have a MTU of 64k
so I wanted these values to be atleast 128 and went for 256 to be sure. 



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------- Additional Comments From pas50 at cam.ac.uk  2002-02-12 04:43 -------
with 64 giving 32k packet
time `cat lapack.ibm.tar.gz | ssh -2 -c 3des-cbc -p 1025 hodgkin  'cat >
f2' `
8.9u 0.7s 1:47 8% 887+629k 0+0io 0pf+0w
with 128 giving 64k packet
time `cat lapack.ibm.tar.gz | ssh -2 -c 3des-cbc -p 1025 hodgkin  'cat >
f2' `
9.0u 0.6s 0:23 41% 895+633k 0+0io 0pf+0w




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------- Additional Comments From markus at openbsd.org  2002-02-13 07:56 -------
hm, ok, lets try this.

keep CHAN_SES_PACKET_DEFAULT fixed:

#define CHAN_SES_PACKET_DEFAULT (16*1024)
and change the _window_ size to

#define CHAN_SES_WINDOW_DEFAULT (CHAN_SES_PACKET_DEFAULT*4)

you can try to increase the 4.

this means the ssh client will send 4 packets before
waiting for an ACK from the server.





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------- Additional Comments From markus at openbsd.org  2002-02-13 10:00 -------
Created an attachment (id=23)
like this




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------- Additional Comments From pas50 at cam.ac.uk  2002-02-13 22:51 -------
time `cat lapack.ibm.tar.gz | local/bin/ssh -2 -c 3des-cbc -p 10222 hodgkin 
'cat > f2' `
8.8u 0.8s 0:23 41% 671+630k 0+0io 137pf+0w
with these changes.



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------- Additional Comments From markus at openbsd.org  2002-02-14 10:20 -------
so, this helps, too?

what happens if you

#define CHAN_SES_WINDOW_DEFAULT (CHAN_SES_PACKET_DEFAULT*20)





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------- Additional Comments From pas50 at cam.ac.uk  2002-02-15 21:10 -------
hartree_a [4] time `cat lapack.ibm.tar.gz | local/bin/ssh -2 -c 3des-cbc -p 1222
hodgkin 'cat > f2' `
8.8u 0.6s 0:23 40% 672+633k 0+0io 140pf+0w

No affect going from 4 to 20. Basically anthing that increases the window
default above 32 helps.



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------- Additional Comments From markus at openbsd.org  2002-02-18 08:43 -------
what about this?

Index: channels.c
==================================================================RCS file:
/cvs/openssh_cvs/channels.c,v
retrieving revision 1.138
diff -u -r1.138 channels.c
--- channels.c  8 Feb 2002 11:07:17 -0000       1.138
+++ channels.c  17 Feb 2002 21:34:48 -0000
@@ -1227,7 +1227,7 @@
 static int
 channel_handle_rfd(Channel *c, fd_set * readset, fd_set * writeset)
 {
-       char buf[16*1024];
+       char buf[64*1024];
        int len;

        if (c->rfd != -1 &&




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------- Additional Comments From pas50 at cam.ac.uk  2002-02-18 21:07 -------
time `cat lapack.ibm.tar.gz | local/bin/ssh -2 -c 3des-cbc -p 10222 hodgkin
'cat
> f2' `
8.8u 0.7s 0:29 33% 681+701k 0+0io 139pf+0w

That didn't seem to help. I checked for reproducability.



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markus at openbsd.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED



------- Additional Comments From markus at openbsd.org  2002-02-19 04:24 -------
there should be no difference between protocol 1 and 2 now.



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