From: Bruce Richardson <bruce.richardson@intel.com>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Cc: Andrew Rybchenko <arybchenko@solarflare.com>,
"Yang, Zhiyong" <zhiyong.yang@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"thomas.monjalon@6wind.com" <thomas.monjalon@6wind.com>
Subject: Re: [dpdk-dev] [RFC] lib/librte_ether: consistent PMD batching behavior
Date: Fri, 20 Jan 2017 11:48:22 +0000 [thread overview]
Message-ID: <20170120114822.GA106360@bricha3-MOBL3.ger.corp.intel.com> (raw)
In-Reply-To: <2601191342CEEE43887BDE71AB9772583F108959@irsmsx105.ger.corp.intel.com>
On Fri, Jan 20, 2017 at 11:24:40AM +0000, Ananyev, Konstantin wrote:
> >
> > From: Andrew Rybchenko [mailto:arybchenko@solarflare.com]
> > Sent: Friday, January 20, 2017 10:26 AM
> > To: Yang, Zhiyong <zhiyong.yang@intel.com>; dev@dpdk.org
> > Cc: thomas.monjalon@6wind.com; Richardson, Bruce <bruce.richardson@intel.com>; Ananyev, Konstantin
> > <konstantin.ananyev@intel.com>
> > Subject: Re: [dpdk-dev] [RFC] lib/librte_ether: consistent PMD batching behavior
> >
> > On 01/20/2017 12:51 PM, Zhiyong Yang wrote:
> > The rte_eth_tx_burst() function in the file Rte_ethdev.h is invoked to
> > transmit output packets on the output queue for DPDK applications as
> > follows.
> >
> > static inline uint16_t
> > rte_eth_tx_burst(uint8_t port_id, uint16_t queue_id,
> > struct rte_mbuf **tx_pkts, uint16_t nb_pkts);
> >
> > Note: The fourth parameter nb_pkts: The number of packets to transmit.
> > The rte_eth_tx_burst() function returns the number of packets it actually
> > sent. The return value equal to *nb_pkts* means that all packets have been
> > sent, and this is likely to signify that other output packets could be
> > immediately transmitted again. Applications that implement a "send as many
> > packets to transmit as possible" policy can check this specific case and
> > keep invoking the rte_eth_tx_burst() function until a value less than
> > *nb_pkts* is returned.
> >
> > When you call TX only once in rte_eth_tx_burst, you may get different
> > behaviors from different PMDs. One problem that every DPDK user has to
> > face is that they need to take the policy into consideration at the app-
> > lication level when using any specific PMD to send the packets whether or
> > not it is necessary, which brings usage complexities and makes DPDK users
> > easily confused since they have to learn the details on TX function limit
> > of specific PMDs and have to handle the different return value: the number
> > of packets transmitted successfully for various PMDs. Some PMDs Tx func-
> > tions have a limit of sending at most 32 packets for every invoking, some
> > PMDs have another limit of at most 64 packets once, another ones have imp-
> > lemented to send as many packets to transmit as possible, etc. This will
> > easily cause wrong usage for DPDK users.
> >
> > This patch proposes to implement the above policy in DPDK lib in order to
> > simplify the application implementation and avoid the incorrect invoking
> > as well. So, DPDK Users don't need to consider the implementation policy
> > and to write duplicated code at the application level again when sending
> > packets. In addition to it, the users don't need to know the difference of
> > specific PMD TX and can transmit the arbitrary number of packets as they
> > expect when invoking TX API rte_eth_tx_burst, then check the return value
> > to get the number of packets actually sent.
> >
> > How to implement the policy in DPDK lib? Two solutions are proposed below.
> >
> > Solution 1:
> > Implement the wrapper functions to remove some limits for each specific
> > PMDs as i40e_xmit_pkts_simple and ixgbe_xmit_pkts_simple do like that.
> >
> > > IMHO, the solution is a bit better since it:
> > > 1. Does not affect other PMDs at all
> > > 2. Could be a bit faster for the PMDs which require it since has no indirect
> > > function call on each iteration
> > > 3. No ABI change
>
> I also would prefer solution number 1 for the reasons outlined by Andrew above.
> Also, IMO current limitation for number of packets to TX in some Intel PMD TX routines
> are sort of artificial:
> - they are not caused by any real HW limitations
> - avoiding them at PMD level shouldn't cause any performance or functional degradation.
> So I don't see any good reason why instead of fixing these limitations in
> our own PMDs we are trying to push them to the upper (rte_ethdev) layer.
>
> Konstantin
>
The main advantage I see is that it should make it a bit easier for
driver writers, since they have a tighter set of constraints to work
with for packet RX and Tx. The routines only have to handle requests for
packets in the range 0-N, rather than not having an upper bound on the
request. It also then saves code duplicating with having multiple
drivers having the same outer-loop code for handling arbitrarily large
requests.
No big deal to me either way though.
/Bruce
next prev parent reply other threads:[~2017-01-20 11:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-20 9:51 Zhiyong Yang
2017-01-20 10:26 ` Andrew Rybchenko
[not found] ` <2601191342CEEE43887BDE71AB9772583F108924@irsmsx105.ger.corp.intel.com>
2017-01-20 11:24 ` Ananyev, Konstantin
2017-01-20 11:48 ` Bruce Richardson [this message]
2017-01-23 16:36 ` Adrien Mazarguil
2017-02-07 7:50 ` Yang, Zhiyong
2017-01-21 4:07 ` Yang, Zhiyong
2017-01-21 4:13 ` Yang, Zhiyong
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