[dpdk-dev] [PATCH 0/9] mbuf: structure reorganization

[Ananyev, Konstantin]

> >
> >
> >
> > > -----Original Message-----
> > > From: Richardson, Bruce
> > > Sent: Thursday, March 30, 2017 1:23 PM
> > > To: Olivier Matz <olivier.matz at 6wind.com>
> > > Cc: dev at dpdk.org; Ananyev, Konstantin <konstantin.ananyev at intel.com>; mb at smartsharesystems.com; Chilikin, Andrey
> > > <andrey.chilikin at intel.com>; jblunck at infradead.org; nelio.laranjeiro at 6wind.com; arybchenko at solarflare.com
> > > Subject: Re: [dpdk-dev] [PATCH 0/9] mbuf: structure reorganization
> > >
> > > On Thu, Mar 30, 2017 at 02:02:36PM +0200, Olivier Matz wrote:
> > > > On Thu, 30 Mar 2017 10:31:08 +0100, Bruce Richardson <bruce.richardson at intel.com> wrote:
> > > > > On Wed, Mar 29, 2017 at 09:09:23PM +0100, Bruce Richardson wrote:
> > > > > > On Wed, Mar 29, 2017 at 05:56:29PM +0200, Olivier Matz wrote:
> > > > > > > Hi,
> > > > > > >
> > > > > > > Does anyone have any other comment on this series?
> > > > > > > Can it be applied?
> > > > > > >
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Olivier
> > > > > > >
> > > > > >
> > > > > > I assume all driver maintainers have done performance analysis to check
> > > > > > for regressions. Perhaps they can confirm this is the case.
> > > > > >
> > > > > > 	/Bruce
> > > > > > >
> > > > > In the absence, of anyone else reporting performance numbers with this
> > > > > patchset, I ran a single-thread testpmd test using 2 x 40G ports (i40e)
> > > > > driver. With RX & TX descriptor ring sizes of 512 or above, I'm seeing a
> > > > > fairly noticable performance drop. I still need to dig in more, e.g. do
> > > > > an RFC2544 zero-loss test, and also bisect the patchset to see what
> > > > > parts may be causing the problem.
> > > > >
> > > > > Has anyone else tried any other drivers or systems to see what the perf
> > > > > impact of this set may be?
> > > >
> > > > I did, of course. I didn't see any noticeable performance drop on
> > > > ixgbe (4 NICs, one port per NIC, 1 core). I can replay the test with
> > > > current version.
> > > >
> > > I had no doubt you did some perf testing! :-)
> > >
> > > Perhaps the regression I see is limited to i40e driver. I've confirmed I
> > > still see it with that driver in zero-loss tests, so next step is to try
> > > and localise what change in the patchset is causing it.
> > >
> > > Ideally, though, I think we should see acks or other comments from
> > > driver maintainers at least confirming that they have tested. You cannot
> > > be held responsible for testing every DPDK driver before you submit work
> > > like this.
> > >
> >
> > Unfortunately  I also see a regression.
> > Did a quick flood test on 2.8 GHZ IVB with 4x10Gb.
> 
> Sorry, forgot to mention - it is on ixgbe.
> So it doesn't look like i40e specific.
> 
> > Observed a drop even with default testpmd RXD/TXD numbers (128/512):
> > from 50.8 Mpps down to 47.8 Mpps.
> > From what I am seeing the particular patch that causing it:
> > [dpdk-dev,3/9] mbuf: set mbuf fields while in pool
> >
> > cc version 5.3.1 20160406 (Red Hat 5.3.1-6) (GCC)
> > cmdline:
> > ./dpdk.org-1705-mbuf1/x86_64-native-linuxapp-gcc/app/testpmd  --lcores='7,8'  -n 4 --socket-mem='1024,0'  -w 04:00.1 -w 07:00.1 -w
> > 0b:00.1 -w 0e:00.1 -- -i
> >

After applying the patch below got nearly original numbers (though not quite) on my box.
dpdk.org mainline:           50.8
with Olivier patch:           47.8
with patch below:            50.4
What I tried to do in it - avoid unnecessary updates of mbuf inside rte_pktmbuf_prefree_seg().
For one segment per packet it seems to help.
Though so far I didn't try it on i40e and didn't do any testing for multi-seg scenario.
Konstantin

$ cat patch.mod4
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index d7af852..558233f 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -1283,12 +1283,28 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
 {
        __rte_mbuf_sanity_check(m, 0);

-       if (likely(rte_mbuf_refcnt_update(m, -1) == 0)) {
+       if (likely(rte_mbuf_refcnt_read(m) == 1)) {
+
+               if (m->next != NULL) {
+                       m->next = NULL;
+                       m->nb_segs = 1;
+               }
+
+               if (RTE_MBUF_INDIRECT(m))
+                       rte_pktmbuf_detach(m);
+
+               return m;
+
+       } else if (rte_atomic16_add_return(&m->refcnt_atomic, -1) == 0) {
+
                if (RTE_MBUF_INDIRECT(m))
                        rte_pktmbuf_detach(m);

-               m->next = NULL;
-               m->nb_segs = 1;
+               if (m->next != NULL) {
+                       m->next = NULL;
+                       m->nb_segs = 1;
+               }
+
                rte_mbuf_refcnt_set(m, 1);

                return m;