LARTC - May 2005 - How to read the TCP congestion window (cwnd) on Linux?

Hi everybody.
Do you know about any way to read the TCP cwnd value (congestion window) 
on Linux?

I have read that on Linux it is not possible to enable a socket option 
(to read to cwnd using the program trpt).

Any way to read the cwnd would be good for me.

thanks

Antonio

Antonio Pinizzotto wrote:
> 
> Hi everybody.
> Do you know about any way to read the TCP cwnd value (congestion window)
> on Linux?
> 
> I have read that on Linux it is not possible to enable a socket option
> (to read to cwnd using the program trpt).
> 
> Any way to read the cwnd would be good for me.
I already answered your question on the end2end list yesterday:
You can get cwnd through the TCP socket monitoring interface using the
"ss"-tool from iproute2 (http://developer.osdl.org/dev/iproute2) or by
getsockopt(TCP_INFO).

Regards
Patrick

On Mon, 02 May 2005 19:22:17 +0200
Antonio Pinizzotto <antonio.pinizzotto@iit.cnr.it> wrote:
> 
> Hi everybody.
> Do you know about any way to read the TCP cwnd value (congestion window) 
> on Linux?
> 
> I have read that on Linux it is not possible to enable a socket option 
> (to read to cwnd using the program trpt).
> 
> Any way to read the cwnd would be good for me.
> 
> thanks
> 
> Antonio
I whipped together a hack using kprobe''s to get graphs for TCP testing.
You can download it from
http://developer.osdl.org/shemminger/prototypes/tcpprobe.tar.gz

Hi Stephen, 
Is this tcpprobe intended for 2.4 kernel?

This is what I get against a 2.6.8-24 kernel: 


/home/ssuciu/tcpprobe/tcpprobe.c: In function
`jtcp_sendmsg'':
/home/ssuciu/tcpprobe/tcpprobe.c:81: warning:
initialization from incompatible pointer type
/home/ssuciu/tcpprobe/tcpprobe.c:83: error: structure
has no member named `snd_nxt''
/home/ssuciu/tcpprobe/tcpprobe.c:83: error: structure
has no member named `snd_una''
/home/ssuciu/tcpprobe/tcpprobe.c:84: error: structure
has no member named `snd_cwnd''
/home/ssuciu/tcpprobe/tcpprobe.c:84: warning: passing
arg 1 of `tcp_current_ssthresh'' from incompatible
pointer type
/home/ssuciu/tcpprobe/tcpprobe.c:85: error: structure
has no member named `snd_wnd''
/home/ssuciu/tcpprobe/tcpprobe.c: In function
`jtcp_recvmsg'':
/home/ssuciu/tcpprobe/tcpprobe.c:100: warning:
initialization from incompatible pointer type
/home/ssuciu/tcpprobe/tcpprobe.c:104: error: structure
has no member named `rcv_nxt''
/home/ssuciu/tcpprobe/tcpprobe.c:104: warning: passing
arg 1 of `tcp_receive_window'' from incompatible
pointer type
make[2]: *** [/home/ssuciu/tcpprobe/tcpprobe.o] Error
1
make[1]: *** [_module_/home/ssuciu/tcpprobe] Error 2
make[1]: Leaving directory `/usr/src/linux-2.6.8-24''

Cheers,
Sorin


--- Stephen Hemminger <shemminger@osdl.org> wrote:
> On Mon, 02 May 2005 19:22:17 +0200
> Antonio Pinizzotto <antonio.pinizzotto@iit.cnr.it>
> wrote:
> 
> > 
> > Hi everybody.
> > Do you know about any way to read the TCP cwnd
> value (congestion window) 
> > on Linux?
> > 
> > I have read that on Linux it is not possible to
> enable a socket option 
> > (to read to cwnd using the program trpt).
> > 
> > Any way to read the cwnd would be good for me.
> > 
> > thanks
> > 
> > Antonio
> 
> I whipped together a hack using kprobe''s to get
> graphs for TCP testing.
> You can download it from
>
http://developer.osdl.org/shemminger/prototypes/tcpprobe.tar.gz
> _______________________________________________
> LARTC mailing list
> LARTC@mailman.ds9a.nl
>
http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
>

On Wed, 4 May 2005 00:54:23 -0700 (PDT)
"Sorin S." <sese_ro@yahoo.com> wrote:
> Hi Stephen, 
> Is this tcpprobe intended for 2.4 kernel?
no, it was built for 2.6.  It could work in 2.4, but you would need
to dig up an old kprobes patch for 2.4 (from ibm), and do some simple
tweaks to the socket to tcp cb mapping.
> 
> This is what I get against a 2.6.8-24 kernel: 
some internal changes to data structures happened about 2.6.10, no big
deal look at tcp_input.c you''ll see how the macros are different

Does that kernel have kprobes?
> 
> 
> /home/ssuciu/tcpprobe/tcpprobe.c: In function
> `jtcp_sendmsg'':
> /home/ssuciu/tcpprobe/tcpprobe.c:81: warning:
> initialization from incompatible pointer type
> /home/ssuciu/tcpprobe/tcpprobe.c:83: error: structure
> has no member named `snd_nxt''
> /home/ssuciu/tcpprobe/tcpprobe.c:83: error: structure
> has no member named `snd_una''
> /home/ssuciu/tcpprobe/tcpprobe.c:84: error: structure
> has no member named `snd_cwnd''
> /home/ssuciu/tcpprobe/tcpprobe.c:84: warning: passing
> arg 1 of `tcp_current_ssthresh'' from incompatible
> pointer type
> /home/ssuciu/tcpprobe/tcpprobe.c:85: error: structure
> has no member named `snd_wnd''
> /home/ssuciu/tcpprobe/tcpprobe.c: In function
> `jtcp_recvmsg'':
> /home/ssuciu/tcpprobe/tcpprobe.c:100: warning:
> initialization from incompatible pointer type
> /home/ssuciu/tcpprobe/tcpprobe.c:104: error: structure
> has no member named `rcv_nxt''
> /home/ssuciu/tcpprobe/tcpprobe.c:104: warning: passing
> arg 1 of `tcp_receive_window'' from incompatible
> pointer type
> make[2]: *** [/home/ssuciu/tcpprobe/tcpprobe.o] Error
> 1
> make[1]: *** [_module_/home/ssuciu/tcpprobe] Error 2
> make[1]: Leaving directory `/usr/src/linux-2.6.8-24''
> 
> Cheers,
> Sorin
> 
> 
> --- Stephen Hemminger <shemminger@osdl.org> wrote:
> > On Mon, 02 May 2005 19:22:17 +0200
> > Antonio Pinizzotto <antonio.pinizzotto@iit.cnr.it>
> > wrote:
> > 
> > > 
> > > Hi everybody.
> > > Do you know about any way to read the TCP cwnd
> > value (congestion window) 
> > > on Linux?
> > > 
> > > I have read that on Linux it is not possible to
> > enable a socket option 
> > > (to read to cwnd using the program trpt).
> > > 
> > > Any way to read the cwnd would be good for me.
> > > 
> > > thanks
> > > 
> > > Antonio
> > 
> > I whipped together a hack using kprobe''s to get
> > graphs for TCP testing.
> > You can download it from
> >
> http://developer.osdl.org/shemminger/prototypes/tcpprobe.tar.gz
> > _______________________________________________
> > LARTC mailing list
> > LARTC@mailman.ds9a.nl
> >
> http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
> >