[ovs-dev] [v6 00/11] MFEX Infrastructure + Optimizations

[Van Haaren, Harry]

> -----Original Message-----
> From: Eelco Chaudron <echaudro at redhat.com>
> Sent: Wednesday, July 7, 2021 9:35 AM
> To: Amber, Kumar <kumar.amber at intel.com>
> Cc: Ferriter, Cian <cian.ferriter at intel.com>; ovs-dev at openvswitch.org;
> fbl at sysclose.org; i.maximets at ovn.org; Van Haaren, Harry
> <harry.van.haaren at intel.com>; Stokes, Ian <ian.stokes at intel.com>
> Subject: Re: [v6 00/11] MFEX Infrastructure + Optimizations
> 
> 
> 
> On 6 Jul 2021, at 17:06, Amber, Kumar wrote:
> 
> > Hi Eelco ,
> >
> >
> > Here is the diff  vor v6 vs v5 :
> >
> > Patch 1 :
> >
> > diff --git a/lib/dpif-netdev-private-extract.c b/lib/dpif-netdev-private-extract.c
> > index 1aebf3656d..4987d628a4 100644
> > --- a/lib/dpif-netdev-private-extract.c
> > +++ b/lib/dpif-netdev-private-extract.c
> > @@ -233,7 +233,7 @@ dpif_miniflow_extract_autovalidator(struct
> dp_packet_batch *packets,
> >                                      uint32_t keys_size, odp_port_t in_port,
> >                                      struct dp_netdev_pmd_thread *pmd_handle)
> >  {
> > -    const size_t cnt = dp_packet_batch_size(packets);
> > +    const uint32_t cnt = dp_packet_batch_size(packets);
> >      uint16_t good_l2_5_ofs[NETDEV_MAX_BURST];
> >      uint16_t good_l3_ofs[NETDEV_MAX_BURST];
> >      uint16_t good_l4_ofs[NETDEV_MAX_BURST];
> > @@ -247,7 +247,7 @@ dpif_miniflow_extract_autovalidator(struct
> dp_packet_batch *packets,
> >          atomic_uintptr_t *pmd_func = (void *)&pmd->miniflow_extract_opt;
> >          atomic_store_relaxed(pmd_func, (uintptr_t) default_func);
> >          VLOG_ERR("Invalid key size supplied, Key_size: %d less than"
> > -                 "batch_size: %ld", keys_size, cnt);
> > +                 "batch_size: %d", keys_size, cnt);
> 
> What was the reason for changing this size_t to uint32_t? Is see other instances
> where %ld is used for logging?
> And other functions like dp_netdev_run_meter() have it as a size_t?

The reason to change this is because 32-bit builds were breaking due to incorrect
format-specifier in the printf. Root cause is because size_t requires different printf
format specifier based on 32 or 64 bit arch.

(As you likely know, size_t is to describe objects in memory, or the return of sizeof operator.
Because 32-bit and 64-bit can have different amounts of memory, size_t can be "unsigned int"
or "unsigned long long").

It does not make sense to me to use a type of variable that changes width based on
architecture to count batch size (a value from 0 to 32).

Simplicity and obvious-ness is nice, and a uint32_t is always exactly what you read it to be,
and %d will always be correct for uint32_t regardless of 32 or 64 bit.

We should not change this back to the more complex and error-prone "size_t", uint32_t is better.

<snip>