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

[Gavin Hu (Arm Technology China)]

> -----Original Message-----
> From: Phil Yang (Arm Technology China)
> Sent: Wednesday, October 10, 2018 5:59 PM
> To: Stephen Hemminger <step...@networkplumber.org>
> Cc: dev@dpdk.org; jerin.ja...@caviumnetworks.com; Gavin Hu (Arm
> Technology China) <gavin...@arm.com>; Honnappa Nagarahalli
> <honnappa.nagaraha...@arm.com>; Ola Liljedahl <ola.liljed...@arm.com>;
> ferruh.yi...@intel.com
> Subject: RE: [dpdk-dev] [PATCH v3 2/4] kni: fix kni fifo synchronization
>
> Hi Hemminger,
>
> > -----Original Message-----
> > From: Stephen Hemminger <step...@networkplumber.org>
> > Sent: Tuesday, October 9, 2018 5:53 AM
> > To: Phil Yang (Arm Technology China) <phil.y...@arm.com>
> > Cc: dev@dpdk.org; jerin.ja...@caviumnetworks.com; Gavin Hu (Arm
> > Technology China) <gavin...@arm.com>; Honnappa Nagarahalli
> > <honnappa.nagaraha...@arm.com>; Ola Liljedahl <ola.liljed...@arm.com>;
> > ferruh.yi...@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.y...@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

I advised a separate patch to make this patch to the point and clean.

-Gavin
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