[X2go-Dev] libssh, nagle, and performance issues

[Mike Gabriel]

Hi Alex,

On Mo 19 Sep 2011 09:51:16 CEST Oleksandr Shneyder wrote:

> Am 17.09.2011 03:39, schrieb John A. Sullivan III:
>> On Fri, 2011-09-16 at 23:17 +0200, Mike Gabriel wrote:
>>> Hi John, hi Alex,
>>>
>>> On Fr 16 Sep 2011 21:56:38 CEST "John A. Sullivan III" wrote:
>>>
>>>> Hello, all.  Since moving to the newer clients using libssh, I've
>>>> noticed what appears to be a performance degradation.  It smells like
>>>> Nagle coalescing packets, e.g., most of the screen will paint, then it
>>>> will pause a moment, and then the rest will paint.  Is there any chance
>>>> we have neglected to disable Nagle when invoking libssh?
>>>>
>>>> This appears to have affected the SNMP over SSH project:
>>>> http://books.google.com/books?id=S62is2vVoVgC&pg=PA29&lpg=PA29&dq=libssh
>>>> +nagle&source=bl&ots=F8Iw-pvQxd&sig=f5dfy0K0ewzSZOhqzTJRSKsDKZ8&hl=en&ei=KppzTrCZD4LJgQeMxLzzDA&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CBwQ6AEwAA#v=onepage&q=libssh%20nagle&f=false
>>>>
>>>> This is in section 4.1. The difference was a latency of over 800ms to
>>>> one of under 60ms.  That seems to be about what I am seeing. There is a
>>>> delay of roughly a second and then the rest of the screen comes through.
>>>> Thanks - John
>>>
>>> Indeed the TCP_NODELAY (which means: turn Nagle off) is not set for
>>> the ssh tunnel in X2goClient. It probably is for the SSH connection
>>> itself, as the SNMP patch has been reported to libssh upstream and
>>> their patch suggestion has been sensible. However, for the SSH tunnels
>>> built up for X2go this TCP_NODELAY option does perhaps not get set.
>>>
>>> @Alex: would this patch fix that in x2goclient???
>>>
>>> diff --git a/sshprocess.cpp b/sshprocess.cpp
>>> index 9e72e8f..03ee9b6 100644
>>> --- a/sshprocess.cpp
>>> +++ b/sshprocess.cpp
>>> @@ -88,6 +88,7 @@ void SshProcess::tunnelLoop()
>>>       const char y=1;
>>>   #endif
>>>       setsockopt(serverSocket, SOL_SOCKET, SO_REUSEADDR,&y, sizeof(int));
>>> +    setsockopt(serverSocket, IPPROTO_TCP, TCP_NODELAY,&y, sizeof(int));
>>>
>>>       address.sin_family=AF_INET;
>>>       address.sin_addr.s_addr=INADDR_ANY;
>
> I don't think that that can be helpful. This part of code is only for
> reverse tunnel which is used for FS forwarding and Pulse Audio.
>

I took another close look at the code of sshProcess.cpp. The patch is  
applied to the method sshProcess::tunnelLoop. This method only gets  
execute in sshProcess::startTunnel.

The call is:

<quote>
if (!reverse)
   tunnelLoop();
else
{
     <blablabla>
}
</quote>

So this makes me think that tunnelLoop() is not for reverse tunneling  
but for the graphics tunnel.

Could you take another look please?

Thanks,
Mike

-- 

DAS-NETZWERKTEAM
mike gabriel, dorfstr. 27, 24245 barmissen
fon: +49 (4302) 281418, fax: +49 (4302) 281419

GnuPG Key ID 0xB588399B
mail: mike.gabriel at das-netzwerkteam.de, http://das-netzwerkteam.de

freeBusy:
https://mail.das-netzwerkteam.de/freebusy/m.gabriel%40das-netzwerkteam.de.xfb
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 490 bytes
Desc: Digitale PGP-Unterschrift
URL: <http://lists.x2go.org/pipermail/x2go-dev/attachments/20110919/d450e473/attachment.pgp>