On Sep 11, 2015 5:55 PM, "Thomas Monjalon" <thomas.monjalon at 6wind.com> wrote: > > 2015-09-11 17:47, Avi Kivity: > > On 09/11/2015 05:25 PM, didier.pallard wrote: > > > On 08/25/2015 08:52 PM, Vlad Zolotarov wrote: > > >> > > >> Helin, the issue has been seen on x540 devices. Pls., see a chapter > > >> 7.2.1.1 of x540 devices spec: > > >> > > >> A packet (or multiple packets in transmit segmentation) can span any > > >> number of > > >> buffers (and their descriptors) up to a limit of 40 minus WTHRESH > > >> minus 2 (see > > >> Section 7.2.3.3 for Tx Ring details and section Section 7.2.3.5.1 for > > >> WTHRESH > > >> details). For best performance it is recommended to minimize the > > >> number of buffers > > >> as possible. > > >> > > >> Could u, pls., clarify why do u think that the maximum number of data > > >> buffers is limited by 8? > > >> > > >> thanks, > > >> vlad > > > > > > Hi vlad, > > > > > > Documentation states that a packet (or multiple packets in transmit > > > segmentation) can span any number of > > > buffers (and their descriptors) up to a limit of 40 minus WTHRESH > > > minus 2. > > > > > > Shouldn't there be a test in transmit function that drops properly the > > > mbufs with a too large number of > > > segments, while incrementing a statistic; otherwise transmit function > > > may be locked by the faulty packet without > > > notification. > > > > > > > What we proposed is that the pmd expose to dpdk, and dpdk expose to the > > application, an mbuf check function. This way applications that can > > generate complex packets can verify that the device will be able to > > process them, and applications that only generate simple mbufs can avoid > > the overhead by not calling the function. > > More than a check, it should be exposed as a capability of the port. > Anyway, if the application sends too much segments, the driver must > drop it to avoid hang, and maintain a dedicated statistic counter to allow > easy debugging.
I agree with Thomas - this should not be optional. Malformed packets should be dropped. In the icgbe case it's a very simple test - it's a single branch per packet so i doubt that it could impose any measurable performance degradation. >
