[dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1 for all NICs but 82598
Thomas Monjalon
thomas.monjalon at 6wind.com
Fri Sep 11 16:55:08 CEST 2015
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.
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