Hi Rahul, > -----Original Message----- > From: Rahul Lakkireddy [mailto:rahul.lakkireddy at chelsio.com] > Sent: Monday, October 05, 2015 1:42 PM > To: Ananyev, Konstantin > Cc: Aaron Conole; dev at dpdk.org; Felix Marti; Kumar A S; Nirranjan > Kirubaharan > Subject: Re: [dpdk-dev] [PATCH 1/6] cxgbe: Optimize forwarding performance > for 40G > > Hi Konstantin, > > On Monday, October 10/05/15, 2015 at 04:46:40 -0700, Ananyev, Konstantin > wrote: > > > > > > > -----Original Message----- > > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Rahul Lakkireddy > > > Sent: Monday, October 05, 2015 11:06 AM > > > To: Aaron Conole > > > Cc: dev at dpdk.org; Felix Marti; Kumar A S; Nirranjan Kirubaharan > > > Subject: Re: [dpdk-dev] [PATCH 1/6] cxgbe: Optimize forwarding > > > performance for 40G > > > > > > Hi Aaron, > > > > > > On Friday, October 10/02/15, 2015 at 14:48:28 -0700, Aaron Conole wrote: > > > > Hi Rahul, > > > > > > > > Rahul Lakkireddy <rahul.lakkireddy at chelsio.com> writes: > > > > > > > > > Update sge initialization with respect to free-list manager > > > > > configuration > > > > > and ingress arbiter. Also update refill logic to refill mbufs only > > > > > after > > > > > a certain threshold for rx. Optimize tx packet prefetch and free. > > > > <<snip>> > > > > > for (i = 0; i < sd->coalesce.idx; i++) { > > > > > - rte_pktmbuf_free(sd->coalesce.mbuf[i]); > > > > > + struct rte_mbuf *tmp = > > > > > sd->coalesce.mbuf[i]; > > > > > + > > > > > + do { > > > > > + struct rte_mbuf *next = > > > > > tmp->next; > > > > > + > > > > > + rte_pktmbuf_free_seg(tmp); > > > > > + tmp = next; > > > > > + } while (tmp); > > > > > sd->coalesce.mbuf[i] = NULL; > > > > Pardon my ignorance here, but rte_pktmbuf_free does this work. I can't > > > > actually see much difference between your rewrite of this block, and > > > > the implementation of rte_pktmbuf_free() (apart from moving your branch > > > > to the end of the function). Did your microbenchmarking really show this > > > > as an improvement? > > > > > > > > Thanks for your time, > > > > Aaron > > > > > > rte_pktmbuf_free calls rte_mbuf_sanity_check which does a lot of > > > checks. > > > > Only when RTE_LIBRTE_MBUF_DEBUG is enabled in your config. > > By default it is switched off. > > Right. I clearly missed this. > I am running with default config only btw. > > > > > > This additional check seems redundant for single segment > > > packets since rte_pktmbuf_free_seg also performs rte_mbuf_sanity_check. > > > > > > Several PMDs already prefer to use rte_pktmbuf_free_seg directly over > > > rte_pktmbuf_free as it is faster. > > > > Other PMDs use rte_pktmbuf_free_seg() as each TD has an associated > > with it segment. So as HW is done with the TD, SW frees associated segment. > > In your case I don't see any point in re-implementing rte_pktmbuf_free() > > manually, > > and I don't think it would be any faster. > > > > Konstantin > > As I mentioned below, I am clearly seeing a difference of 1 Mpps. And 1 > Mpps is not a small difference IMHO.
Agree with you here - it is a significant difference. > > When running l3fwd with 8 queues, I also collected a perf report. > When using rte_pktmbuf_free, I see that it eats up around 6% cpu as > below in perf top report:- > -------------------- > 32.00% l3fwd [.] cxgbe_poll > 22.25% l3fwd [.] t4_eth_xmit > 20.30% l3fwd [.] main_loop > 6.77% l3fwd [.] rte_pktmbuf_free > 4.86% l3fwd [.] refill_fl_usembufs > 2.00% l3fwd [.] write_sgl > ..... > -------------------- > > While, when using rte_pktmbuf_free_seg directly, I don't see above > problem. perf top report now comes as:- > ------------------- > 33.36% l3fwd [.] cxgbe_poll > 32.69% l3fwd [.] t4_eth_xmit > 19.05% l3fwd [.] main_loop > 5.21% l3fwd [.] refill_fl_usembufs > 2.40% l3fwd [.] write_sgl > .... > ------------------- I don't think these 6% disappeared anywhere. As I can see, now t4_eth_xmit() increased by roughly same amount (you still have same job to do). To me it looks like in that case compiler didn't really inline rte_pktmbuf_free(). Wonder can you add 'always_inline' attribute to the rte_pktmbuf_free(), and see would it make any difference? Konstantin > > I obviously missed the debug flag for rte_mbuf_sanity_check. > However, there is a clear difference of 1 Mpps. I don't know if its the > change between while construct used in rte_pktmbuf_free and the > do..while construct that I used - is making the difference. > > > > > > > > > > The forwarding perf. improvement with only this particular block is > > > around 1 Mpps for 64B packets when using l3fwd with 8 queues. > > > > > > Thanks, > > > Rahul
