From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yong Wang Subject: Re: [PATCH 1/5] vmxnet3: Fix VLAN Rx stripping Date: Wed, 29 Oct 2014 17:57:59 +0000 Message-ID: References: <1413181389-14887-1-git-send-email-yongwang@vmware.com> <20141029090449.GA8292@BRICHA3-MOBL> <1988013.IRBMoDeiJN@xps13> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: "dev-VfR2kkLFssw@public.gmane.org" To: Thomas Monjalon , Bruce Richardson Return-path: In-Reply-To: <1988013.IRBMoDeiJN@xps13> Content-Language: en-US Content-ID: <32861E0D0DB92F49B35152D26AAC08A4-xOhs/FgTdIXLi+/K9TH57EEOCMrvLtNR@public.gmane.org> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces-VfR2kkLFssw@public.gmane.org Sender: "dev" 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. Yong On 10/29/14, 2:41 AM, "Thomas Monjalon" 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" >> > wrote: >> >=20 >> >=20 >> > >On Mon, 13 Oct 2014 18:42:18 +0000 >> > >Yong Wang 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. >> >=20 >> > 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? >> >=20 >>=20 >> We can look to do that, but we need to beware of performance >>regressions if=20 >> we do so. Certainly the vector implementation of the ixgbe would be >>severely=20 >> impacted performance-wise if such a change were made. However, code >>paths=20 >> which are not as highly tuned, or which do not need to be as highly >>tuned=20 >> could perhaps use the standard function. >>=20 >> The main reason for this regression is that reset will clear all fields >>of=20 >> the mbuf, which would be wasted cycles for a number of the PMDs as they >>will=20 >> later set some of the fields based on values in the receive descriptor. >>=20 >> Basically, on descriptor rearm in a PMD, the only fields that need to >>be=20 >> 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. > >--=20 >Thomas