On Monday, October 10/05/15, 2015 at 20:37:31 +0530, Rahul Lakkireddy wrote: > On Monday, October 10/05/15, 2015 at 07:09:27 -0700, Ananyev, Konstantin > wrote: > > Hi Rahul, > > [...] > > > > > > 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). > > Right. > > > 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 will try out above and update further. >
Tried always_inline and didn't see any difference in performance in RHEL 6.4 with gcc 4.4.7, but was seeing 1 MPPS improvement with the above block. I've moved to latest RHEL 7.1 with gcc 4.8.3 and tried both always_inline and the above block and I'm not seeing any difference for both. Will drop this block and submit a v2. Thanks for the review Aaron and Konstantin. Thanks, Rahul
