Messages in this thread | | | Date | Mon, 11 Feb 2019 10:45:58 +0200 | From | Mika Westerberg <> | Subject | Re: [PATCH v2 14/28] thunderbolt: Extend tunnel creation to more than 2 adjacent switches |
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On Sun, Feb 10, 2019 at 04:33:28PM +0100, Lukas Wunner wrote: > On Wed, Feb 06, 2019 at 04:17:24PM +0300, Mika Westerberg wrote: > > Now that we can allocate hop IDs per port on a path, we can take > > advantage of this and create tunnels covering longer paths than just > > between two adjacent switches. PCIe actually does not need this as it is > > always a daisy chain between two adjacent switches but this way we do > > not need to hard-code creation of the tunnel. > > That doesn't seem to be correct, at the bottom of this page there's > a figure showing a PCI tunnel between non-adjacent switches (blue line): > > https://developer.apple.com/library/archive/documentation/HardwareDrivers/Conceptual/ThunderboltDevGuide/Basics/Basics.html > > I'm not sure if there are advantages to such tunnels: Reduced latency > perhaps because packets need not pass through PCIe adapters on the > in-between device? Or maybe this allows for more fine-grained traffic > prioritization?
Interesting.
Are you sure Apple actually uses setup like that? I think I have never seen such configuration happening on any of the devices I have.
I can update the changelog to mention that if you think it is useful. Something like below maybe?
PCIe actually does not need this as it is typically a daisy chain between two adjacent switches but this way we do not need to hard-code creation of the tunnel.
> > + i = 0; > > + tb_for_each_port(in_port, src, dst) > > + i++; > > This looks more complicated than necessary. Isn't the path length > always the length of the route string from in_port switch to out_port > switch, plus 2 for the adapter on each end? Or do paths without > adapters exist?
Yes, I think you are right.
> > + for (i = 0; i < num_hops; i++) { > > + in_port = tb_port_get_next(src, dst, out_port); > > + > > + if (in_port->dual_link_port && in_port->link_nr != link_nr) > > + in_port = in_port->dual_link_port; > > + > > + ret = tb_port_alloc_in_hopid(in_port, in_hopid, -1); > > + if (ret < 0) > > + goto err; > > + in_hopid = ret; > > + > > + out_port = tb_port_get_next(src, dst, in_port); > > + if (!out_port) > > + goto err; > > There's a NULL pointer check here, but the invocation of tb_port_get_next() > further up to assign in_port lacks such a check. Is it guaranteed to never > be NULL?
No, I'll add NULL check there.
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