[dpdk-dev] [PATCH v3 2/4] kni: fix kni fifo synchronization

Phil Yang (Arm Technology China) Phil.Yang at arm.com
Wed Oct 10 11:58:47 CEST 2018


Hi Hemminger,

> -----Original Message-----
> From: Stephen Hemminger <stephen at networkplumber.org>
> Sent: Tuesday, October 9, 2018 5:53 AM
> To: Phil Yang (Arm Technology China) <Phil.Yang at arm.com>
> Cc: dev at dpdk.org; jerin.jacob at caviumnetworks.com; Gavin Hu (Arm
> Technology China) <Gavin.Hu at arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli at arm.com>; Ola Liljedahl <Ola.Liljedahl at arm.com>;
> ferruh.yigit at intel.com
> Subject: Re: [dpdk-dev] [PATCH v3 2/4] kni: fix kni fifo synchronization
>
> On Mon,  8 Oct 2018 17:11:44 +0800
> Phil Yang <phil.yang at arm.com> wrote:
>
> > diff --git a/lib/librte_kni/rte_kni_fifo.h
> > b/lib/librte_kni/rte_kni_fifo.h index ac26a8c..70ac14e 100644
> > --- a/lib/librte_kni/rte_kni_fifo.h
> > +++ b/lib/librte_kni/rte_kni_fifo.h
> > @@ -28,8 +28,9 @@ kni_fifo_put(struct rte_kni_fifo *fifo, void **data,
> > unsigned num)  {
> >  unsigned i = 0;
> >  unsigned fifo_write = fifo->write;
> > -unsigned fifo_read = fifo->read;
> >  unsigned new_write = fifo_write;
> > +rte_smp_rmb();
> > +unsigned fifo_read = fifo->read;
> >
>
> The patch makes sense, but this function should be changed to match kernel
> code style.
> That means no declarations after initial block, and use 'unsigned int' rather than
> 'unsigned'
>
> Also. why is i initialized? Best practice now is to not do gratitious initialization
> since it defeats compiler checks for accidental  use of uninitialized variables.
>
> What makes sense is something like:
>
> kni_fifo_put(struct rte_kni_fifo *fifo, void **data, unsigned num) {
> unsigned int i, fifo_read, fifo_write, new_write;
>
> fifo_write = fifo->write;
> new_write = fifo_write;
> rte_smb_rmb();
> fifo_read = fifo->read;
>
> Sorry, blaming you for issues which are inherited from original KNI code.
> Maybe someone should run kernel checkpatch (not DPDK checkpatch) on it and
> fix those.

Thanks for your comment.

I think I can submit a new separate patch to fix this historical issue.

Thanks,
Phil Yang
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