DPDK patches and discussions
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From: Thomas Monjalon <thomas.monjalon@6wind.com>
To: "Iremonger, Bernard" <bernard.iremonger@intel.com>
Cc: "Richardson, Bruce" <bruce.richardson@intel.com>,
	dev@dpdk.org, "Doherty, Declan" <declan.doherty@intel.com>,
	"Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	"Mcnamara, John" <john.mcnamara@intel.com>
Subject: Re: [dpdk-dev] [PATCH v3 3/4] bonding: take queue spinlock in rx/tx burst functions
Date: Thu, 16 Jun 2016 20:38:11 +0200	[thread overview]
Message-ID: <1632739.trvk2NaClS@xps13> (raw)
In-Reply-To: <8CEF83825BEC744B83065625E567D7C21A03A6D7@IRSMSX108.ger.corp.intel.com>

2016-06-16 16:41, Iremonger, Bernard:
> Hi Thomas,
> <snip>
> > 2016-06-16 15:32, Bruce Richardson:
> > > On Mon, Jun 13, 2016 at 01:28:08PM +0100, Iremonger, Bernard wrote:
> > > > > Why does this particular PMD need spinlocks when doing RX and TX,
> > > > > while other device types do not? How is adding/removing devices
> > > > > from a bonded device different to other control operations that
> > > > > can be done on physical PMDs? Is this not similar to say bringing
> > > > > down or hotplugging out a physical port just before an RX or TX
> > operation takes place?
> > > > > For all other PMDs we rely on the app to synchronise control and
> > > > > data plane operation - why not here?
> > > > >
> > > > > /Bruce
> > > >
> > > > This issue arose during VM live migration testing.
> > > > For VM live migration it is necessary (while traffic is running) to be able to
> > remove a bonded slave device, stop it, close it and detach it.
> > > > It a slave device is removed from a bonded device while traffic is running
> > a segmentation fault may occur in the rx/tx burst function. The spinlock has
> > been added to prevent this occurring.
> > > >
> > > > The bonding device already uses a spinlock to synchronise between the
> > add and remove functionality and the slave_link_status_change_monitor
> > code.
> > > >
> > > > Previously testpmd did not allow, stop, close or detach of PMD while
> > > > traffic was running. Testpmd has been modified with the following
> > > > patchset
> > > >
> > > > http://dpdk.org/dev/patchwork/patch/13472/
> > > >
> > > > It now allows stop, close and detach of a PMD provided in it is not
> > forwarding and is not a slave of bonded PMD.
> > > >
> > > I will admit to not being fully convinced, but if nobody else has any
> > > serious objections, and since this patch has been reviewed and acked,
> > > I'm ok to merge it in. I'll do so shortly.
> > 
> > Please hold on.
> > Seeing locks introduced in the Rx/Tx path is an alert.
> > We clearly need a design document to explain where locks can be used and
> > what are the responsibility of the control plane.
> > If everybody agrees in this document that DPDK can have some locks in the
> > fast path, then OK to merge it.
> > 
> > So I would say NACK for 16.07 and maybe postpone to 16.11.
> 
> Looking at the documentation for the bonding PMD.
> 
> http://dpdk.org/doc/guides/prog_guide/link_bonding_poll_mode_drv_lib.html
> 
> In section 10.2 it states the following:
> 
> Bonded devices support the dynamical addition and removal of slave devices using the rte_eth_bond_slave_add / rte_eth_bond_slave_remove APIs.
> 
> If a slave device is added or removed while traffic is running, there is the possibility of a segmentation fault in the rx/tx burst functions. This is most likely to occur in the round robin bonding mode.
> 
> This patch set fixes what appears to be a bug in the bonding PMD.

It can be fixed by removing this statement in the doc.

One of the design principle of DPDK is to avoid locks.

> Performance measurements have been made with this patch set applied and without the patches applied using 64 byte packets. 
> 
> With the patches applied the following drop in performance was observed:
> 
> % drop for fwd+io:	0.16%
> % drop for fwd+mac:	0.39%
> 
> This patch set has been reviewed and ack'ed, so I think it should be applied in 16.07

I understand your point of view and I gave mine.
Now we need more opinions from others.

  reply	other threads:[~2016-06-16 18:38 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-05 15:14 [dpdk-dev] [PATCH 0/5] bonding: locks Bernard Iremonger
2016-05-05 15:14 ` [dpdk-dev] [PATCH 1/5] bonding: replace spinlock with read/write lock Bernard Iremonger
2016-05-05 17:12   ` Stephen Hemminger
2016-05-06 10:32     ` Declan Doherty
2016-05-06 15:55       ` Stephen Hemminger
2016-05-13 17:10         ` Ananyev, Konstantin
2016-05-13 17:18           ` Ananyev, Konstantin
2016-05-26 16:24             ` Iremonger, Bernard
2016-05-05 15:14 ` [dpdk-dev] [PATCH 2/5] bonding: add read/write lock to rx/tx burst functions Bernard Iremonger
2016-05-05 15:14 ` [dpdk-dev] [PATCH 3/5] bonding: remove memcopy of slaves from rx/tx burst function Bernard Iremonger
2016-05-05 15:14 ` [dpdk-dev] [PATCH 4/5] bonding: add read/write lock to stop function Bernard Iremonger
2016-05-05 15:15 ` [dpdk-dev] [PATCH 5/5] bonding: add read/write lock to the link_update function Bernard Iremonger
2016-05-26 16:38 ` [dpdk-dev] [PATCH v2 0/6] bonding: locks Bernard Iremonger
2016-05-26 16:38   ` [dpdk-dev] [PATCH v2 1/6] bonding: add spinlock to rx and tx queues Bernard Iremonger
2016-06-10 18:12     ` Ananyev, Konstantin
2016-06-12 17:11     ` [dpdk-dev] [PATCH v3 0/4] bonding: locks Bernard Iremonger
2016-06-12 17:11       ` [dpdk-dev] [PATCH v3 1/4] bonding: add spinlock to rx and tx queues Bernard Iremonger
2016-06-12 17:11       ` [dpdk-dev] [PATCH v3 2/4] bonding: grab queue spinlocks in slave add and remove Bernard Iremonger
2016-06-12 17:11       ` [dpdk-dev] [PATCH v3 3/4] bonding: take queue spinlock in rx/tx burst functions Bernard Iremonger
2016-06-13  9:18         ` Bruce Richardson
2016-06-13 12:28           ` Iremonger, Bernard
2016-06-16 14:32             ` Bruce Richardson
2016-06-16 15:00               ` Thomas Monjalon
2016-06-16 16:41                 ` Iremonger, Bernard
2016-06-16 18:38                   ` Thomas Monjalon [this message]
2017-02-15 18:01                     ` Ferruh Yigit
2017-02-16  9:13                       ` Bruce Richardson
2017-02-16 11:39                         ` Iremonger, Bernard
2017-02-20 11:15                           ` Ferruh Yigit
2016-09-09 11:29         ` Ferruh Yigit
2016-06-12 17:11       ` [dpdk-dev] [PATCH v3 4/4] bonding: remove memcpy from " Bernard Iremonger
2016-09-11 12:39         ` Yuanhan Liu
2016-05-26 16:38   ` [dpdk-dev] [PATCH v2 2/6] bonding: grab queue spinlocks in slave add and remove Bernard Iremonger
2016-06-10 18:14     ` Ananyev, Konstantin
2016-05-26 16:38   ` [dpdk-dev] [PATCH v2 3/6] bonding: take queue spinlock in rx/tx burst functions Bernard Iremonger
2016-06-10 18:14     ` Ananyev, Konstantin
2016-05-26 16:38   ` [dpdk-dev] [PATCH v2 4/6] bonding: add spinlock to stop function Bernard Iremonger
2016-05-26 16:38   ` [dpdk-dev] [PATCH v2 5/6] bonding: add spinlock to link update function Bernard Iremonger
2016-05-26 16:38   ` [dpdk-dev] [PATCH v2 6/6] bonding: remove memcpy from burst functions Bernard Iremonger
2016-06-10 18:15     ` Ananyev, Konstantin
2016-06-10 14:45   ` [dpdk-dev] [PATCH v2 0/6] bonding: locks Bruce Richardson
2016-06-10 18:24     ` Iremonger, Bernard

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