DPDK patches and discussions
 help / color / mirror / Atom feed
From: Yong Wang <yongwang@vmware.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>,
	Bruce Richardson <bruce.richardson@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 1/5] vmxnet3: Fix VLAN Rx stripping
Date: Wed, 29 Oct 2014 17:57:59 +0000	[thread overview]
Message-ID: <D07677ED.23355%yongwang@vmware.com> (raw)
In-Reply-To: <1988013.IRBMoDeiJN@xps13>

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" <thomas.monjalon@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@networkplumber.org>
>> > wrote:
>> > 
>> > 
>> > >On Mon, 13 Oct 2014 18:42:18 +0000
>> > >Yong Wang <yongwang@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.
>
>-- 
>Thomas

  reply	other threads:[~2014-10-29 17:49 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-13  6:23 [dpdk-dev] [PATCH 0/5] vmxnet3 pmd fixes/improvement Yong Wang
2014-10-13  6:23 ` [dpdk-dev] [PATCH 1/5] vmxnet3: Fix VLAN Rx stripping Yong Wang
2014-10-13  9:31   ` Stephen Hemminger
2014-10-13 18:42     ` Yong Wang
2014-10-22 13:39       ` Stephen Hemminger
2014-10-28 21:57         ` Yong Wang
2014-10-29  9:04           ` Bruce Richardson
2014-10-29  9:41             ` Thomas Monjalon
2014-10-29 17:57               ` Yong Wang [this message]
2014-10-29 18:51                 ` Thomas Monjalon
2014-10-13  6:23 ` [dpdk-dev] [PATCH 2/5] vmxnet3: Add VLAN Tx offload Yong Wang
2014-10-13  6:23 ` [dpdk-dev] [PATCH 3/5] vmxnet3: Fix dev stop/restart bug Yong Wang
2014-10-13  6:23 ` [dpdk-dev] [PATCH 4/5] vmxnet3: Add rx pkt check offloads Yong Wang
2014-10-13  6:23 ` [dpdk-dev] [PATCH 5/5] vmxnet3: Some perf improvement on the rx path Yong Wang
2014-11-05  0:13   ` Thomas Monjalon
2014-10-13 20:29 ` [dpdk-dev] [PATCH 0/5] vmxnet3 pmd fixes/improvement Thomas Monjalon
2014-10-13 21:00   ` Yong Wang
2014-10-21 22:10     ` Yong Wang
2014-10-22  7:07       ` Cao, Waterman
2014-10-28 14:40         ` Thomas Monjalon
2014-10-28 19:59           ` Yong Wang
2014-10-29  0:33             ` Cao, Waterman
2014-11-05  1:32     ` Cao, Waterman
2014-11-04  5:57 ` Zhang, XiaonanX
2014-11-04 22:50   ` Thomas Monjalon
2014-11-05  5:26     ` Cao, Waterman

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=D07677ED.23355%yongwang@vmware.com \
    --to=yongwang@vmware.com \
    --cc=bruce.richardson@intel.com \
    --cc=dev@dpdk.org \
    --cc=thomas.monjalon@6wind.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).