[dpdk-dev] eventdev: sw rx adapter enqueue caching

Jerin Jacob Kollanukkaran jerinj at marvell.com
Tue May 7 14:13:52 CEST 2019

+ Nikhil

Please add respective maintainer from MAINTAINERS file for quick resolution.

> -----Original Message-----
> From: dev <dev-bounces at dpdk.org> On Behalf Of Elo, Matias (Nokia -
> FI/Espoo)
> Sent: Tuesday, May 7, 2019 5:33 PM
> To: Mattias Rönnblom <hofors at lysator.liu.se>
> Cc: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; dev at dpdk.org;
> nd <nd at arm.com>
> Subject: Re: [dpdk-dev] eventdev: sw rx adapter enqueue caching
> On 7 May 2019, at 15:01, Mattias Rönnblom
> <hofors at lysator.liu.se<mailto:hofors at lysator.liu.se>> wrote:
> On 2019-05-07 13:12, Honnappa Nagarahalli wrote:
> Hi,
> The SW eventdev rx adapter has an internal enqueue buffer 'rx_adapter-
> event_enqueue_buffer', which stores packets received from the NIC until at
> least BATCH_SIZE (=32) packets have been received before enqueueing them to
> eventdev. For example in case of validation testing, where often a small number
> of specific test packets is sent to the NIC, this causes a lot of problems. One
> would always have to transmit at least BATCH_SIZE test packets before anything
> can be received from eventdev. Additionally, if the rx packet rate is slow this
> also adds a considerable amount of additional delay.
> Looking at the rx adapter API and sw implementation code there doesn’t seem
> to be a way to disable this internal caching. In my opinion this “functionality"
> makes testing sw rx adapter so cumbersome that either the implementation
> should be modified to enqueue the cached packets after a while (some
> performance penalty) or there should be some method to disable caching. Any
> opinions how this issue could be fixed?
> At the minimum, I would think there should be a compile time option.
> From a use case perspective, I think it falls under latency vs throughput
> considerations. If there is a latency sensitive application, it might not want to
> wait till 32 packets are received.
> From what I understood from Matias Elo and also after a quick glance in the
> code, the unlucky packets will be buffered indefinitely, in case the system goes
> idle. This is totally unacceptable (both in production and validation), in my
> opinion, and should be filed as a bug.
> Indeed, this is what happens. I’ll create a bug report to track this issue.

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