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From: Olivier MATZ <olivier.matz@6wind.com>
To: John McNamara <john.mcnamara@intel.com>, dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2 3/4] examples: example showing use of callbacks.
Date: Mon, 16 Feb 2015 15:33:40 +0100	[thread overview]
Message-ID: <54E1FFC4.1060605@6wind.com> (raw)
In-Reply-To: <1423841989-9090-4-git-send-email-john.mcnamara@intel.com>

Hi John,

On 02/13/2015 04:39 PM, John McNamara wrote:
> From: Richardson, Bruce <bruce.richardson@intel.com>
> 
> Example showing how callbacks can be used to insert a timestamp
> into each packet on RX. On TX the timestamp is used to calculate
> the packet latency through the app, in cycles.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>


I'm looking at the example and I don't understand what is the advantage
of having callbacks in ethdev layer, knowing that the application can
do the same job by a standard function call.

What is the advantage of having callbacks compared to:


for (port = 0; port < nb_ports; port++) {
	struct rte_mbuf *bufs[BURST_SIZE];
	const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
			bufs, BURST_SIZE);
	if (unlikely(nb_rx == 0))
		continue;
	add_timestamp(bufs, nb_rx);

	const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
			bufs, nb_rx);
	calc_latency(bufs, nb_tx);

	if (unlikely(nb_tx < nb_rx)) {
		uint16_t buf;
		for (buf = nb_tx; buf < nb_rx; buf++)
			rte_pktmbuf_free(bufs[buf]);
	}
}


To me, doing like the code above has several advantages:

- code is more readable: the callback is explicitly invoked, so there is
  no risk to forget it
- code is faster: the functions calls can be inlined by the compiler
- easier to handle error cases in the callback function as the error
  code is accessible to the application
- there is no need to add code in ethdev api to do this
- if the application does not want to use callbacks (I suppose most
  applications), it won't have any performance impact

Regards,
Olivier

  parent reply	other threads:[~2015-02-16 14:33 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-22 16:47 [dpdk-dev] [PATCH RFC 0/3] DPDK ethdev callback support Bruce Richardson
2014-12-22 16:47 ` [dpdk-dev] [PATCH RFC 1/3] ethdev: rename callbacks field to intr_cbs Bruce Richardson
2014-12-22 16:47 ` [dpdk-dev] [PATCH RFC 2/3] ethdev: Add in data rxtx callback support Bruce Richardson
2014-12-22 16:47 ` [dpdk-dev] [PATCH RFC 3/3] examples: example showing use of callbacks Bruce Richardson
2014-12-22 17:02 ` [dpdk-dev] [PATCH RFC 0/3] DPDK ethdev callback support Thomas Monjalon
2014-12-22 17:33   ` Bruce Richardson
2014-12-22 17:47     ` Neil Horman
2014-12-23  9:28       ` Bruce Richardson
2014-12-23 13:09         ` Neil Horman
2014-12-23 14:09           ` Bruce Richardson
2015-01-05 16:17     ` Bruce Richardson
2014-12-22 18:31 ` Stephen Hemminger
2014-12-23  9:29   ` Bruce Richardson
2014-12-23  4:23 ` Vithal S Mohare
2014-12-23  9:30   ` Bruce Richardson
2014-12-23  9:37     ` Vithal S Mohare
2014-12-24  1:43       ` Zhang, Helin
2014-12-24  5:06 ` Qiu, Michael
2015-02-12 19:57 ` [dpdk-dev] [PATCH " John McNamara
2015-02-12 19:57   ` [dpdk-dev] [PATCH 1/3] ethdev: rename callbacks field to intr_cbs John McNamara
2015-02-12 19:57   ` [dpdk-dev] [PATCH 2/3] ethdev: Add in data rxtx callback support John McNamara
2015-02-12 21:12     ` Neil Horman
2015-02-12 19:57   ` [dpdk-dev] [PATCH 3/3] examples: example showing use of callbacks John McNamara
2015-02-13 14:54   ` [dpdk-dev] [PATCH 0/3] DPDK ethdev callback support Declan Doherty
2015-02-13 15:39 ` [dpdk-dev] [PATCH v2 0/4] " John McNamara
2015-02-13 15:39   ` [dpdk-dev] [PATCH v2 1/4] ethdev: rename callbacks field to intr_cbs John McNamara
2015-02-13 16:06     ` Thomas Monjalon
2015-02-13 16:52       ` Thomas Monjalon
2015-02-13 15:39   ` [dpdk-dev] [PATCH v2 2/4] ethdev: Add in data rxtx callback support John McNamara
2015-02-13 16:33     ` Thomas Monjalon
2015-02-13 17:49       ` Bruce Richardson
2015-02-13 15:39   ` [dpdk-dev] [PATCH v2 3/4] examples: example showing use of callbacks John McNamara
2015-02-13 16:02     ` Thomas Monjalon
2015-02-16 14:33     ` Olivier MATZ [this message]
2015-02-16 15:16       ` Bruce Richardson
2015-02-16 17:34         ` Thomas Monjalon
2015-02-17 12:17           ` Declan Doherty
2015-02-17 12:25           ` Bruce Richardson
2015-02-17 13:28             ` Olivier MATZ
2015-02-17 13:50               ` Bruce Richardson
2015-02-17 15:49                 ` Neil Horman
2015-02-17 16:00                   ` Bruce Richardson
2015-02-17 16:08                     ` Neil Horman
2015-02-17 16:15                       ` Bruce Richardson
2015-02-17 19:27                         ` Neil Horman
2015-02-17 15:32             ` Thomas Monjalon
2015-02-17 15:58               ` Bruce Richardson
2015-02-13 15:39   ` [dpdk-dev] [PATCH v2 4/4] abi: Added rxtx callback functions to ABI versioning John McNamara
2015-02-13 15:59     ` Thomas Monjalon
2015-02-13 15:48   ` [dpdk-dev] [PATCH v2 0/4] DPDK ethdev callback support Declan Doherty
2015-02-18 17:42 ` [dpdk-dev] [PATCH v3 0/3] " John McNamara
2015-02-18 17:42   ` [dpdk-dev] [PATCH v3 1/3] ethdev: Rename callbacks field to link_intr_cbs John McNamara
2015-02-18 17:42   ` [dpdk-dev] [PATCH v3 2/3] ethdev: Add rxtx callback support John McNamara
2015-02-18 18:19     ` Thomas Monjalon
2015-02-19  9:33       ` Mcnamara, John
2015-02-18 17:42   ` [dpdk-dev] [PATCH v3 3/3] examples: example showing use of callbacks John McNamara
2015-02-19 17:56   ` [dpdk-dev] [PATCH v4 0/3] DPDK ethdev callback support John McNamara
2015-02-19 17:56     ` [dpdk-dev] [PATCH v4 1/3] ethdev: rename callbacks field to link_intr_cbs John McNamara
2015-02-19 17:56     ` [dpdk-dev] [PATCH v4 2/3] ethdev: add optional rxtx callback support John McNamara
2015-02-20 10:06       ` Bruce Richardson
2015-02-20 10:31         ` Thomas Monjalon
2015-02-19 17:56     ` [dpdk-dev] [PATCH v4 3/3] examples: example showing use of callbacks John McNamara
2015-02-20 17:03   ` [dpdk-dev] [PATCH v5 0/3] DPDK ethdev callback support John McNamara
2015-02-20 17:03     ` [dpdk-dev] [PATCH v5 1/3] ethdev: rename callbacks field to link_intr_cbs John McNamara
2015-02-20 17:03     ` [dpdk-dev] [PATCH v5 2/3] ethdev: add optional rxtx callback support John McNamara
2015-02-23 15:11       ` Thomas Monjalon
2015-02-23 17:27         ` Mcnamara, John
2015-02-20 17:03     ` [dpdk-dev] [PATCH v5 3/3] examples: example showing use of callbacks John McNamara
2015-02-23 18:30   ` [dpdk-dev] [PATCH v6 0/3] DPDK ethdev callback support John McNamara
2015-02-23 18:30     ` [dpdk-dev] [PATCH v6 1/3] ethdev: rename callbacks field to link_intr_cbs John McNamara
2015-02-23 18:30     ` [dpdk-dev] [PATCH v6 2/3] ethdev: add optional rxtx callback support John McNamara
2015-02-23 18:30     ` [dpdk-dev] [PATCH v6 3/3] examples: example showing use of callbacks John McNamara
2015-02-23 23:39     ` [dpdk-dev] [PATCH v6 0/3] DPDK ethdev callback support Thomas Monjalon

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