2014-10-29 17:57, Yong Wang: > Sounds good to me but it does look like the rte_rxmbuf_alloc() could use > some comments to make it explicit that rte_pktmbuf_reset() is avoided by > design for the reasons that Bruce described. Furthermore, > rte_rxmbuf_alloc() is duplicated in almost all the pmd drivers. Will it > make sense to promote it to a public API? Just a thought.
Yes, it makes sense. > On 10/29/14, 2:41 AM, "Thomas Monjalon" <thomas.monjalon at 6wind.com> wrote: > > >2014-10-29 09:04, Bruce Richardson: > >> On Tue, Oct 28, 2014 at 09:57:14PM +0000, Yong Wang wrote: > >> > On 10/22/14, 6:39 AM, "Stephen Hemminger" <stephen at networkplumber.org> > >> > wrote: > >> > > >> > > >> > >On Mon, 13 Oct 2014 18:42:18 +0000 > >> > >Yong Wang <yongwang at vmware.com> wrote: > >> > > > >> > >> Are you referring to the patch as a whole or your comment is about > >>the > >> > >>reset of vlan_tci on the "else" (no vlan tags stripped) path? I am > >>not > >> > >>sure I get your comments here. This patch simply fixes a bug on > >>the rx > >> > >>vlan stripping path (where valid vlan_tci stripped is overwritten > >> > >>unconditionally later on the rx path in the original vmxnet3 pmd > >> > >>driver). All the other pmd drivers are doing the same thing in > >>terms of > >> > >>translating descriptor status to rte_mbuf flags for vlan stripping. > >> > > > >> > >I was thinking that there are many fields in a pktmbuf and rather > >>than > >> > >individually > >> > >setting them (like tci). The code should call the common > >> > >rte_pktmbuf_reset before setting > >> > >the fields. That way when someone adds a field to mbuf they don't > >>have > >> > >to chasing > >> > >through every driver that does it's own initialization. > >> > > >> > Currently rte_pktmbuf_reset() is used in rte_pktmbuf_alloc() but looks > >> > like most pmd drivers use rte_rxmbuf_alloc() to replenish rx buffers, > >> > which directly calls __rte_mbuf_raw_alloc > >> > () without calling rte_pktmbuf_reset(). How about we change that in a > >> > separate patch to all pmd drivers so that we can keep their behavior > >> > consistent? > >> > > >> > >> We can look to do that, but we need to beware of performance > >>regressions if > >> we do so. Certainly the vector implementation of the ixgbe would be > >>severely > >> impacted performance-wise if such a change were made. However, code > >>paths > >> which are not as highly tuned, or which do not need to be as highly > >>tuned > >> could perhaps use the standard function. > >> > >> The main reason for this regression is that reset will clear all fields > >>of > >> the mbuf, which would be wasted cycles for a number of the PMDs as they > >>will > >> later set some of the fields based on values in the receive descriptor. > >> > >> Basically, on descriptor rearm in a PMD, the only fields that need to > >>be > >> reset would be those not set by the copy of data from the descriptor. > > > >This is typically a trade-off situation. > >I think that we should prefer the performance.
