Hi Ferruh, > -----Original Message----- > From: Richardson, Bruce > Sent: Thursday, February 16, 2017 9:14 AM > To: Yigit, Ferruh <ferruh.yi...@intel.com> > Cc: Thomas Monjalon <thomas.monja...@6wind.com>; Iremonger, Bernard > <bernard.iremon...@intel.com>; Ananyev, Konstantin > <konstantin.anan...@intel.com>; Doherty, Declan > <declan.dohe...@intel.com>; DPDK <dev@dpdk.org> > Subject: Re: [dpdk-dev] [PATCH v3 3/4] bonding: take queue spinlock in rx/tx > burst functions > > On Wed, Feb 15, 2017 at 06:01:45PM +0000, Ferruh Yigit wrote: > > On 6/16/2016 7:38 PM, thomas.monjalon at 6wind.com (Thomas Monjalon) > wrote: > > > 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_li > > >> b.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. > > > > > > > Hi, > > > > These patches are sitting in the patchwork for a long time. Discussion > > never concluded and patches kept deferred each release. > > > > I think we should give a decision about them: > > > > 1- We can merge them in this release, they are fixing a valid problem, > > and patches are already acked. > > > > 2- We can reject them, if not having them for more than six months not > > caused a problem, perhaps they are not really that required. And if > > somebody needs them in the future, we can resurrect them from > patchwork. > > > > I vote for option 2, any comments? > > > +1 on option 2. There are obviously not badly needed if nobody is asking > for them for over six months. > > /Bruce
I am ok with option 2, provided they can be retrieved if needed. Regards, Bernard.
