[dpdk-dev] [PATCH 01/39] examples/l2fwd: convert to new ethdev offloads API

Andrew Rybchenko arybchenko at solarflare.com
Mon Nov 27 08:40:13 CET 2017


On 11/27/2017 10:03 AM, Shahaf Shuler wrote:
>
> Monday, November 27, 2017 8:35 AM, Andrew Rybchenko:
>
> Yes this is right. Not exposing the CRC offload flag means the device 
> don’t support CRC strip toggling, however it does not explicitly say 
> if device always strip/not.
>
> I guess device that has such limitation should specify it on the 
> “Limitation” section of the PMD guide.
>
> If it is interpreted in such way it sounds like loss of functionality.
> Don't think it is a good way to rely on documentation here. It should
> be more reliable way. PMD still can check if offload is not enabled and
> complain, but there is no way to say that it is strictly required.
> As I understand similar things are covered with so-called fixed offloads
> in Linux.
>
> Can you elaborate which functionality is being lost here?
>
> If your suggestion is for the PMD to force the CRC STRIP offload in 
> case it is not supporting **not** to strip CRC then I am OK with that.
>

[AR] I mean that if we say that no CRC strip offload set means either 
strip or not-strip it is bad. Application and transmit part may rely on 
Ethernet CRC presence. My suggestion is to provide a way to say that CRC 
striping (and any other offload) cannot be disabled.
>
> Yes it is.
>
> With the new Tx offloads API the application can choose the Tx 
> offloads it wants to use according to its needs.
>
> For l2fwd case – it doesn’t use any of them. Any default txq flag the 
> PMD set there is irrelevant.
>
> What I tried to do is not to preserve the entire old behavior rather 
> to evolve the examples/applications while keeping the same 
> functionality (i.e. the offloads which the application use are set, 
> the rest are not).
>
>
> That's true for checksum and VLAN offloads, but false for fast-free.
> As I understand l2fwd and many other examples meet fast-free
> requirements and if PMD supports it, it should be used since it will
> show better performance results.
>
> I agree about the Fast free offload. However IMO such optimization can 
> be introduced on other series which further more optimize the 
> performance of such applications, what do you think?
>

[AR] If so, it is definitely a loss of functionality here. Since before 
the patch PMD can provide default TxQ flags and usage of these flags 
will allow an application to see the best performance. (Yes, if it was 
bad if application blindly use these flags). May be it should be covered 
by separate patches, but hanging it in the air for a long time is bad. I 
definitely would like to hear more opinions here from example 
application and PMD maintainers.


More information about the dev mailing list