From: Bruce Richardson <bruce.richardson@intel.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH RFC 0/3] DPDK ethdev callback support
Date: Mon, 5 Jan 2015 16:17:56 +0000 [thread overview]
Message-ID: <20150105161755.GA5356@bricha3-MOBL3> (raw)
In-Reply-To: <20141222173306.GA11568@bricha3-MOBL3>
On Mon, Dec 22, 2014 at 05:33:07PM +0000, Bruce Richardson wrote:
> On Mon, Dec 22, 2014 at 06:02:53PM +0100, Thomas Monjalon wrote:
> > Hi Bruce,
> >
> > Callbacks, as hooks for applications, give more flexibility and are
> > generally a good idea.
> > In DPDK the main issue will be to avoid performance degradation.
> > I see you use "unlikely" for callback branching.
> > Could we reduce more the impact of this test by removing the queue array,
> > i.e. having port-wide callbacks instead of per-queue callbacks?
>
> I can give that a try, but I don't see it making much difference if any. The
> main thing to avoid with branching is branch mis-prediction, which should not
> be a problem here, as the user is not going to be adding or removing callbacks
> between each RX and TX call, making the branches highly predictable - i.e. always
> go the same way.
> The reason for using per-queue callbacks is that I think we can do more with
> it that way. For instance, if we want to do some additional processing or
> calculations on only IP traffic, then we can use hardware offloads on most
> NICs to steer the IP traffic to a separate queue and only apply the callbacks
> to that queue. If the performance is the same, I think we should therefore keep
> the per-queue version.
>
I tried just using a single callback pointer per port, instead of per-queue.
Performance looked the same for the no-callback case, the case of an empty
callback function, and the test application with callbacks for latency
computation.
> >
> > 2014-12-22 16:47, Bruce Richardson:
> > > Future extensions: in future the ethdev library can be extended to provide
> > > a standard set of callbacks for use by drivers.
> >
> > Having callbacks for drivers seems strange to me.
> > If drivers need to accomplish some tasks, they do it by implementing an
> > ethdev service. New services are declared for new needs.
> > Callbacks are the reverse logic. Why should it be needed?
>
> Typo, I meant for applications! Drivers don't need them indeed.
>
> >
> > > For now this patch set is RFC and still needs additional work for creating
> > > a remove function for callbacks and to add in additional testing code.
> > > Since this adds in new code into the critical data path, I have run some
> > > performance tests using testpmd with the ixgbe vector drivers (i.e. the
> > > fastest, fast-path we have :-) ). Performance drops due to this patch
> > > seems minimal to non-existant, rough tests on my system indicate a drop
> > > of perhaps 1%.
> > >
> > > All feedback welcome.
> >
> > It would be good to have more performance tests with different configurations.
>
> Sure, if you have ideals for specific tests you'd like to see I'll try and
> get some numbers. What I did look as was the performance impact for this patch
> without actually putting in place any callbacks, and the worst-case here is
> hardly noticable. For an empty callback, i.e. the pure callback overhead, the
> performance should still be in low single-digit percentages, but I'll test to
> confirm that. For other slower RX and TX paths, e.g. those using scattered
> packets, or with TX offloads, the performance impact will be even less.
>
I modified the sample app in patch 3 of this set to have empty callbacks on
both RX and TX, and the performance impact vs the non-callback case was again
about 1% only. [Again using the vector RX/TX fastpath functions, with 4 ports
handled by a single lcore].
Regards,
/Bruce
next prev parent reply other threads:[~2015-01-05 16:18 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-22 16:47 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 [this message]
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
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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