Re: [dpdk-dev] [PATCH 2/3] pmd: RX function need keep EXTERNAL_MBUF flag

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Oct 24, 2014 at 10:46:06AM +0000, Ananyev, Konstantin wrote:
> Hi Changchun,
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ouyang Changchun
> > Sent: Friday, October 24, 2014 9:10 AM
> > To: dev@dpdk.org
> > Subject: [dpdk-dev] [PATCH 2/3] pmd: RX function need keep EXTERNAL_MBUF flag
> > 
> > Every pmd RX function need keep the EXTERNAL_MBUF flag
> > in mbuf.ol_flags, and can't overwrite it when filling ol_flags from
> > descriptor to mbuf, otherwise, it probably cause to crash when freeing a mbuf
> > and trying to freeing its attached external buffer, say, from guest space.
> > 
> 
> Don't really like the idea to put:
> mb->ol_flags = pkt_flags | (mb->ol_flags & EXTERNAL_MBUF); 
> in each and every PMD from now on...
> 
> From other side, it is probably not very good that RX functions update whole ol_flags, not only RX related part.
> Wonder can we reserve low 32bits of ol_flags for RX, and high 32bits for TX and generic stuff.
> So our ol_flags will look something like that:
> 
> union {
> 	uint64_t ol_raw_flags;
> 	struct {
> 		uint32_t rx;
> 		uint32_t gen_tx;
> 	} ol_flags
> };
> 
> And make all PMD RX functions to operate on rx part of the flags only:
> mb->ol_flags.rx = pkt_flags;
> ?
> 
> Konstantin
>
I would tend to agree with this. Changchun, did you get to assess the 
performance impact of making this change to the PMDs? I suspect that making 
the changes to each PMD would impact performance, while Konstantin's 
suggestion should eliminate that impact.
The downside there is that we are limiting the flexibility we have in 
expanding beyond 32 RX flags and 24 TX flags. :-(

/Bruce