Re: [dpdk-dev] possible kni bug and proposed fix

[ALeX Wang <ee07b291@gmail.com>]

On 17 May 2016 at 03:07, Ferruh Yigit <ferruh.yigit@intel.com> wrote:

> On 5/16/2016 4:31 PM, ALeX Wang wrote:
> > Hi Ferruh,
> >
> > Thx for pointing out the 'fill alloc_q with these mubfs _until it gets
> > full_.',
> >
> > I saw the size of all queues are 'KNI_FIFO_COUNT_MAX (1024)'...
> > The corresponding memory required is more than what I specify as
> > 'socket_mem' (since i'm using VM)...
> >
>
> If the mempool is not big enough to fill the ring, this explains the
> error log. Logic is to fill the alloc_q, but if you are missing the
> required mbufs, in each rte_kni_rx_burst() it will complain about memory.
>
> But the required memory for mbufs to fill the ring is not too much. It
> should be ~2Mbytes, are you sure you are missing this much memory?
>
>

Thx for reminding me about this, by default, i only allocate 2048 mbufs for
my
pool...  once i raise it to 4096, the issue is gone...  will the
`KNI_FIFO_COUNT_MAX `
ever change?  I want to try adding some documentation,...


> > Also, in my use case, I only `tcpreplay` through the kni interface, and
> > my application only do rx and then free the 'mbufs'.  So there is no tx
> > at all.
> >
> > So, in my case, I still think this is a bug/defect, or somewhere i still
> > misunderstand,
> >
> > P.S. The description here seems to be inverted,
> >
> http://dpdk.org/doc/api/rte__kni_8h.html#a0cdd727cdc227d005fef22c0189f3dfe
> > 'rte_kni_rx_burst' does the 'It handles allocating the mbufs for KNI
> > interface alloc queue.'
> >
>
> You are right. That part of the description for rte_kni_rx_burst and
> rte_kni_tx_burst needs to be replaced. Do you want to send a patch?
>
>
Sure, will do that,

Thanks,
Alex Wang,



> > Thanks,
> > Alex Wang,
> >
> > On 16 May 2016 at 04:20, Ferruh Yigit <ferruh.yigit@intel.com
> > <mailto:ferruh.yigit@intel.com>> wrote:
> >
> >     On 5/15/2016 5:48 AM, ALeX Wang wrote:
> >     > Hi,
> >     >
> >     > When using the kni module to test my application inside
> >     > debian (virtualbox) VM (kernel version 4.4), I get the
> >     >
> >     > "KNI: Out of memory"
> >     >
> >     > from syslog every time I `tcpreply` packets through
> >     > the kni interface.
> >     >
> >     > After checking source code, I saw that when I call
> >     > 'rte_kni_rx_burst()', no matter how many packets
> >     > are actually retrieved, we always call 'kni_allocate_mbufs()'
> >     > and try allocate 'MAX_MBUF_BURST_NUM' more
> >     > mbufs...  I fix the issue via using this patch below,
> >     >
> >     > Could you confirm if this is an actual bug?
> >     >
> >
> >     Hi Alex,
> >
> >     I don't think this is a bug.
> >
> >     kni_allocate_mbufs() will allocate MAX_MBUF_BURST_NUM mbufs as you
> >     mentioned. And will fill alloc_q with these mubfs _until it gets
> full_.
> >     And if the alloc_q is full and there are remaining mbufs, they will
> be
> >     freed. So for some cases this isn't the most optimized way, but
> there is
> >     no defect.
> >
> >     Since you are getting "KNI: Out of memory", somewhere else can be
> >     missing freeing mbufs.
> >
> >     mbufs freeing done in rte_kni_tx_burst(), I can guess two cases that
> can
> >     cause problem:
> >     a) not calling rte_kni_tx_burst() frequent, so that all free mbufs
> >     consumed.
> >     b) calling rte_kni_tx_burst() with number of mbufs bigger than
> >     MAX_MBUF_BURST_NUM, because this function frees at most
> >     MAX_MBUF_BURST_NUM of mbufs, but if you are calling calling
> >     rte_kni_tx_burst() with bigger numbers, this will cause mbufs to
> stuck
> >     in free_q
> >
> >
> >     Regards,
> >     ferruh
> >
> >
> >
> >
> >
> > --
> > Alex Wang,
> > Open vSwitch developer
>
>


-- 
Alex Wang,
Open vSwitch developer