On Wed, May 18, 2016 at 05:43:00PM +0100, Bruce Richardson wrote: > On Wed, May 18, 2016 at 07:27:43PM +0530, Jerin Jacob wrote: > > To avoid multiple stores on fast path, Ethernet drivers > > aggregate the writes to data_off, refcnt, nb_segs and port > > to an uint64_t data and write the data in one shot > > with uint64_t* at &mbuf->rearm_data address. > > > > Some of the non-IA platforms have store operation overhead > > if the store address is not naturally aligned.This patch > > fixes the performance issue on those targets. > > > > Signed-off-by: Jerin Jacob <jerin.jacob at caviumnetworks.com> > > --- > > > > Tested this patch on IA and non-IA(ThunderX) platforms. > > This patch shows 400Kpps/core improvement on ThunderX + ixgbe + vector > > environment. > > and this patch does not have any overhead on IA platform. > > > > Have tried an another similar approach by replacing "buf_len" with "pad" > > (in this patch context), > > Since it has additional overhead on read and then mask to keep "buf_len" > > intact, > > not much improvement is not shown. > > ref: http://dpdk.org/ml/archives/dev/2016-May/038914.html > > > > --- > While this will work and from your tests doesn't seem to have a performance > impact, I'm not sure I particularly like it. It's extending out the end of > cacheline0 of the mbuf by 16 bytes, though I suppose it's not technically > using > up any more space of it.
Extending by 2 bytes. Right ?. Yes, I guess, Now we using only 56 out of 64 bytes in the first 64-byte cache line. > > What I'm wondering about though, is do we have any usecases where we need a > variable buf_len for packets for RX. These mbufs come directly from a mempool, > which is generally understood to be a set of fixed-sized buffers. I realise > that > this change was made in the past after some discussion, but one of the key > points > there [at least to my reading] was that - even though nobody actually made a > concrete case where they had variable-sized buffers - having support for them > made no performance difference. > > The latter part of that has now changed, and supporting variable-sized mbufs > from an mbuf pool has a perf impact. Do we definitely need that functionality, > because the easiest fix here is just to move the rxrearm marker back above > mbuf_len as it was originally in releases like 1.8? And initialize the buf_len with mp->elt_size - sizeof(struct rte_mbuf). Right? I don't have a strong opinion on this, I can do this if there is no objection on this. Let me know. However, I do see in future, "buf_len" may belong at the end of the first 64 byte cache line as currently "port" is defined as uint8_t, IMO, that is less. We may need to increase that uint16_t. The reason why I think that because, Currently in ThunderX HW, we do have 128VFs per socket for built-in NIC, So, the two node configuration and one external PCIe NW card configuration can easily go beyond 256 ports. > > Regards, > /Bruce > > Ref: http://dpdk.org/ml/archives/dev/2014-December/009432.html >
