Re: [dpdk-dev] [PATCH 1/1] mbuf: move pool pointer in first half

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

On Sat, Nov 07, 2020 at 07:57:05PM +0100, Morten Brørup wrote:
> > From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > Sent: Saturday, November 7, 2020 4:53 PM
> > 
> > The mempool pointer in the mbuf struct is moved
> > from the second to the first half.
> > It should increase performance on most systems having 64-byte cache line,
> > i.e. mbuf is split in two cache lines.
> 
> Perhaps with the #define DEV_TX_OFFLOAD_MBUF_FAST_FREE mentioned by Konstantin, it might be better moving m->next instead, at least for applications with the opportunity to set this flag (e.g. applications with only one mbuf pool).
> 
> Unfortunately, the information about the DEV_TX_OFFLOAD_MBUF_FAST_FREE flag came to light after the techboard meeting, and I don't have any benchmarks to support this suggestion, so I guess it's hard to change the techboard's decision to move the pool pointer.
> 

The thing with FAST_FREE is that it doesn't just indicate that there is
only one mbuf pool, but rather that none of the packets are chained mbufs
either. Therefore, the flag applies equally to both next and pool pointers
for optimization. [And the flag should perhaps be two flags!]

/Bruce