> -----Original Message----- > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Bruce Richardson > Sent: Monday, June 15, 2015 2:44 PM > To: Olivier MATZ > Cc: dev at dpdk.org; Damjan Marion (damarion) > Subject: Re: [dpdk-dev] rte_mbuf.next in 2nd cacheline > > On Mon, Jun 15, 2015 at 03:20:22PM +0200, Olivier MATZ wrote: > > Hi Damjan, > > > > On 06/10/2015 11:47 PM, Damjan Marion (damarion) wrote: > > > > > > Hi, > > > > > > We noticed 7% performance improvement by simply moving rte_mbuf.next > > > field to the 1st cache line. > > > > > > Currently, it falls under /* second cache line - fields only used in slow > > > path or on TX */ > > > but it is actually used at several places in rx fast path. (e.g.: > > > i40e_rx_alloc_bufs() is setting that field to NULL). > > > > > > Is there anything we can do here (stop using next field, or move it to > > > 1st cache line)? > > > > Agree, this is also something I noticed, see: > > http://dpdk.org/ml/archives/dev/2015-February/014400.html > > > > I did not have the time to do performance testing, but it's something > > I'd like to do as soon as I can. I don't see any obvious reason not to > > do it. > > > > It seems we currently just have enough room to do it (8 bytes are > > remaining in the first cache line when compiled in 64 bits). > > This, to me, is the obvious reason not to do it! It prevents us from taking in > any other offload fields in the RX fast-path into the mbuf. > > That being said, I can see why we might want to look to move it - but from the > work done in the ixgbe driver, I'd be hopeful we can get as much performance > with > it on the second cache line for most cases, through judicious use of > prefetching, > or otherwise. > > It took a lot of work and investigation to get free space in the mbuf - > especially > in cache line 0, and I'd like to avoid just filling the cache line up again as > long as we possibly can!
Yep, agree with Bruce here. Plus, with packet_type going to be 4B and vlan_tci_outer, we just don't have 8 free bytes at the first cache line any more. Konstantin > > /Bruce > > > > > > > Regards, > > Olivier > > > > > > > > > > Thanks, > > > > > > Damjan > > > > > > > > > > > >
