DPDK patches and discussions
 help / color / mirror / Atom feed
From: Bruce Richardson <bruce.richardson@intel.com>
To: Morten Brørup <mb@smartsharesystems.com>
Cc: "Zhao1, Wei" <wei.zhao1@intel.com>,
	"Guo, Jia" <jia.guo@intel.com>,
	dev@dpdk.org, Thomas Monjalon <thomas@monjalon.net>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	Andrew Rybchenko <arybchenko@solarflare.com>
Subject: Re: [dpdk-dev] ixgbe vector rx does not conform torte_eth_rx_burst() API
Date: Fri, 17 Jul 2020 14:49:03 +0100
Message-ID: <20200717134903.GG708@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35C61128@smartserver.smartshare.dk>

On Thu, Jul 16, 2020 at 11:08:49AM +0200, Morten Brørup wrote:
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zhao1, Wei
> > Sent: Thursday, July 16, 2020 10:50 AM
> > 
> > Hi,
> > 
> > > -----Original Message-----
> > > From: Morten Brørup <mb@smartsharesystems.com>
> > > Sent: Thursday, July 16, 2020 12:03 AM
> > > To: Zhao1, Wei <wei.zhao1@intel.com>; Guo, Jia <jia.guo@intel.com>
> > > Cc: dev@dpdk.org; Thomas Monjalon <thomas@monjalon.net>; Yigit,
> > Ferruh
> > > <ferruh.yigit@intel.com>; Andrew Rybchenko
> > <arybchenko@solarflare.com>
> > > Subject: ixgbe vector rx does not conform to rte_eth_rx_burst() API
> > >
> > > Wei, Jeff,
> > >
> > > For the ixgbe driver using vector functions, i.e.
> > ixgbe_recv_pkts_vec(), calling
> > > rte_eth_rx_burst() with nb_pkts > RTE_IXGBE_MAX_RX_BURST only returns
> > > RTE_IXGBE_MAX_RX_BURST packets. E.g. calling rte_eth_rx_burst() with
> > > nb_pkts=64 only returns 32 packets.
> > >
> > >
> > > The API description of rte_eth_rx_burst() says:
> > >
> > > <quote>
> > > The rte_eth_rx_burst() function returns the number of packets
> > actually
> > > retrieved, which is the number of rte_mbuf data structures
> > effectively supplied
> > > into the rx_pkts array. A return value equal to nb_pkts indicates
> > that the RX
> > > queue contained at least rx_pkts packets, and this is likely to
> > signify that other
> > > received packets remain in the input queue. Applications implementing
> > a
> > > "retrieve as much received packets as possible" policy can check this
> > specific
> > > case and keep invoking the rte_eth_rx_burst() function until a value
> > less than
> > > nb_pkts is returned.
> > > </quote>
> > >
> > > The driver implementation does not conform to the documented behavior
> > for
> > > "retrieve as much received packets as possible" applications.
> > 
> > It seems not an issue, this function has comment bellow, it is design
> > work in that way.
> > 
> > 
> > /*
> >  * vPMD receive routine, only accept(nb_pkts >=
> > RTE_IXGBE_DESCS_PER_LOOP)
> >  *
> >  * Notice:
> >  * - nb_pkts < RTE_IXGBE_DESCS_PER_LOOP, just return no packet
> >  * - nb_pkts > RTE_IXGBE_MAX_RX_BURST, only scan RTE_IXGBE_MAX_RX_BURST
> >  *   numbers of DD bit
> >  * - floor align nb_pkts to a RTE_IXGBE_DESC_PER_LOOP power-of-two
> >  */
> > 
> 
> I noticed this already. And yes, ixgbe_recv_pkts_vec() does what its comments says.
> 
> However, when ixgbe_recv_pkts_vec() is used as the driver's implementation of the rte_eth_rx_burst() function call, the rte_eth_rx_burst() function does not do what is expected of the rte_eth_rx_burst() function.
> 
> The implementation must conform to the API that it implements.
> 
> If you don't want to update the ixgbe_recv_pkts_vec() function, I propose that you add a wrapper function that calls ixgbe_recv_pkts_vec() repeatedly, and use the wrapper function as the implementation of the rte_eth_rx_burst() function.
>
I agree it does not conform to the API as documented. Looking at the i40e
AVX2 vector code paths, the regular (no-fragmented packets) path does not
seem to put a limit on the size of burst received, while the scattered
receive path uses the latter scheme of a wrapper function. Therefore,
either approach should work for ixgbe driver, I think.

/Bruce

  reply	other threads:[~2020-07-17 13:49 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 16:02 [dpdk-dev] ixgbe vector rx does not conform to rte_eth_rx_burst() API Morten Brørup
2020-07-16  8:49 ` Zhao1, Wei
2020-07-16  9:08   ` [dpdk-dev] ixgbe vector rx does not conform torte_eth_rx_burst() API Morten Brørup
2020-07-17 13:49     ` Bruce Richardson [this message]
2020-07-18  3:32     ` Zhao1, Wei
2020-07-18  3:44       ` Zhao1, Wei
2020-07-27  9:42         ` [dpdk-dev] ixgbe vector rx does not conform to rte_eth_rx_burst() API Morten Brørup
2020-07-27 10:35           ` Zhao1, Wei

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=20200717134903.GG708@bricha3-MOBL.ger.corp.intel.com \
    --to=bruce.richardson@intel.com \
    --cc=arybchenko@solarflare.com \
    --cc=dev@dpdk.org \
    --cc=ferruh.yigit@intel.com \
    --cc=jia.guo@intel.com \
    --cc=mb@smartsharesystems.com \
    --cc=thomas@monjalon.net \
    --cc=wei.zhao1@intel.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

DPDK patches and discussions

This inbox may be cloned and mirrored by anyone:

	git clone --mirror https://inbox.dpdk.org/dev/0 dev/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dev dev/ https://inbox.dpdk.org/dev \
		dev@dpdk.org
	public-inbox-index dev

Example config snippet for mirrors.
Newsgroup available over NNTP:
	nntp://inbox.dpdk.org/inbox.dpdk.dev


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git