re: [PATCH] new timeout behavior for RPC requests on TCP sockets

[Richard B. Johnson]

On Wed, 13 Nov 2002, Chuck Lever wrote:

> On Tue, 12 Nov 2002, Dan Kegel wrote:
> 
> > Chuck wrote:
> > > make RPC timeout behavior over TCP sockets behave more like reference
> > > client implementations.  reference behavior is to transmit the same
> > > request three times at 60 second intervals; if there is no response, close
> > > and reestablish the socket connection.  we modify the Linux RPC client as
> > > follows:
> > >
> > > +  after a minor retransmit timeout, use the same timeout value when
> > >    retrying on a TCP socket rather than doubling the value
> > > +  after a major retransmit timeout, close the socket and attempt
> > >    to reestablish a fresh TCP connection
> > >
> > > note that today mount uses a 6 second timeout with 5 retries for NFS over
> > > TCP by default; proper default behavior is 2 retries each with 60 second
> > > timeouts.  a separate patch for mount is pending.
> >
> > Chuck, can you briefly explain why RPC does any minor
> > retransmits at all over TCP?
> > Shouldn't TCP's natural retransmit take care of that?
> 
> the socket layer guarantees delivery only to the RPC server application...
> if the application itself chooses to drop the request, an RPC retransmit
> is still required.
> 
> 	- Chuck Lever
> --

If the application "chooses to drop the request", the kernel is not
required to fix that application. The RPC cannot retransmit if
it has been shut-down or disconnected, which is about the only
way the application could "choose to drop the request". So something
doesn't smell right here.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
   Bush : The Fourth Reich of America