From: Ferruh Yigit <ferruh.yigit@intel.com> To: Morten Brørup <mb@smartsharesystems.com>, Bruce Richardson <bruce.richardson@intel.com> Cc: thomas@monjalon.net, arybchenko@solarflare.com, jia.guo@intel.com, dev@dpdk.org Subject: Re: [dpdk-dev] [PATCH] ethdev: rte_eth_rx_burst() nb_pktsrequirements Date: Tue, 13 Oct 2020 11:55:51 +0100 Message-ID: <60d87dbf-167e-d0a6-781a-5f54ee5cb5ac@intel.com> (raw) In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35C612DF@smartserver.smartshare.dk> On 9/14/2020 1:42 PM, Morten Brørup wrote: >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Bruce Richardson >> Sent: Monday, September 14, 2020 1:27 PM >> >> On Mon, Sep 14, 2020 at 01:05:11PM +0200, Morten Brørup wrote: >>> Updated description of rte_eth_rx_burst() to reflect what drivers, >>> when using vector instructions, expect from nb_pkts. >>> >>> Also discussed on the mailing list here: >>> >> http://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35C61257@smarts >> erver.smartshare.dk/ >>> >>> Signed-off-by: Morten Brørup <mb@smartsharesystems.com> >>> --- >>> lib/librte_ethdev/rte_ethdev.h | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/lib/librte_ethdev/rte_ethdev.h >> b/lib/librte_ethdev/rte_ethdev.h >>> index 70295d7ab..41f8ba4ef 100644 >>> --- a/lib/librte_ethdev/rte_ethdev.h >>> +++ b/lib/librte_ethdev/rte_ethdev.h >>> @@ -4469,6 +4469,10 @@ int >> rte_eth_dev_hairpin_capability_get(uint16_t port_id, >>> * burst-oriented optimizations in both synchronous and asynchronous >>> * packet processing environments with no overhead in both cases. >>> * >>> + * @note >>> + * Some drivers using vector instructions require that *nb_pkts* >> is >>> + * divisible by 4 or 8, depending on the driver implementation. >>> + * >> >> Not technically true, in that the drivers will round the value down to >> the >> nearest multiple of 4 or 8. So how about rewording as: >> >> "Some drivers using vector instructions may round the *nb_pkts* driver >> to >> a multiple of 4 or 8 depending upon the driver implementation." >> > > You are correct about the driver behavior. > > However, if you pass nb_pkts=9, the driver will return 8 packets, > and thus it does not conform to the API behavior of returning nb_pkts > if they are there. > > This is why the description in this patch differs from the description we reached in the RFC discussion. > Hi Morten, Bruce, +1 to document the this behavior. But in the patch the wording is more strict: "... require that *nb_pkts* is divisible by 4 or 8 ..." "... The value must be divisible by 8 in order to work with any driver." I am not sure the requirement is that strict. Application still provide any value for 'nb_pkts', so the value doesn't "have to" be divisible 8/4. But for vector PMD case it will return number of packets round down to 8/4. Perhaps can add for vector PMD it must be at least 4/8? Bruce's explanation sound more accurate to me, what do you think? >>> * The rte_eth_rx_burst() function does not provide any error >>> * notification to avoid the corresponding overhead. As a hint, the >>> * upper-level application might check the status of the device link >> once >>> @@ -4485,6 +4489,7 @@ int rte_eth_dev_hairpin_capability_get(uint16_t >> port_id, >>> * must be large enough to store *nb_pkts* pointers in it. >>> * @param nb_pkts >>> * The maximum number of packets to retrieve. >>> + * The value must be divisible by 8 in order to work with any >> driver. >> >> Similarly here, I think it's better to state that it should be at least >> 8, >> and any values not divisible by 8 may be rounded down. >> >>> * @return >>> * The number of packets actually retrieved, which is the number >>> * of pointers to *rte_mbuf* structures effectively supplied to >> the >>> -- >>> 2.17.1 >>> >
next prev parent reply other threads:[~2020-10-13 10:56 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-14 11:05 [dpdk-dev] [PATCH] ethdev: rte_eth_rx_burst() nb_pkts requirements Morten Brørup 2020-09-14 11:26 ` Bruce Richardson 2020-09-14 12:42 ` [dpdk-dev] [PATCH] ethdev: rte_eth_rx_burst() nb_pktsrequirements Morten Brørup 2020-10-13 10:55 ` Ferruh Yigit [this message] 2020-10-14 8:26 ` [dpdk-dev] [PATCH] ethdev: rte_eth_rx_burst()nb_pktsrequirements Morten Brørup 2020-10-14 8:53 ` Thomas Monjalon 2020-10-14 9:29 ` Bruce Richardson 2020-10-14 11:14 ` Morten Brørup 2020-10-14 11:38 ` Bruce Richardson 2020-10-15 7:36 ` Morten Brørup 2020-10-26 15:06 ` [dpdk-dev] [PATCH] ethdev: rte_eth_rx_burst() nb_pkts requirements Morten Brørup 2020-10-26 15:15 ` Ajit Khaparde 2020-10-27 10:24 ` Bruce Richardson 2020-10-30 9:27 ` Ferruh Yigit
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