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From: Ruifeng Wang <Ruifeng.Wang@arm.com>
To: Jerin Jacob <jerinjacobk@gmail.com>
Cc: "jerinj@marvell.com" <jerinj@marvell.com>,
	"hemant.agrawal@nxp.com" <hemant.agrawal@nxp.com>,
	Ferruh Yigit <ferruh.yigit@intel.com>,
	"thomas@monjalon.net" <thomas@monjalon.net>,
	David Marchand <david.marchand@redhat.com>,
	dpdk-dev <dev@dpdk.org>, nd <nd@arm.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH 1/4] examples/l3fwd: tune prefetch for better performance
Date: Wed, 19 May 2021 07:52:59 +0000
Message-ID: <AM5PR0802MB246584E47CB99CEDD6472F3C9E2B9@AM5PR0802MB2465.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <CALBAE1PiXCypP1=d5t1L+JovQgh882AUWNtkV48Fka+evDYskQ@mail.gmail.com>

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Wednesday, April 14, 2021 2:51 AM
> To: Ruifeng Wang <Ruifeng.Wang@arm.com>
> Cc: jerinj@marvell.com; hemant.agrawal@nxp.com; Ferruh Yigit
> <ferruh.yigit@intel.com>; thomas@monjalon.net; David Marchand
> <david.marchand@redhat.com>; dpdk-dev <dev@dpdk.org>; nd
> <nd@arm.com>; Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Subject: Re: [dpdk-dev] [PATCH 1/4] examples/l3fwd: tune prefetch for
> better performance
> 
> On Thu, Mar 18, 2021 at 3:56 PM Ruifeng Wang <ruifeng.wang@arm.com>
> wrote:
> >
> > Packet header is prefetched before packet processing for better memory
> > access performance. As L2 header will be updated by l3fwd, using of
> > prefetch for store hint will set cache line to proper status and
> > reduce cache maintenance overhead.
> 
> The code does read the cache line too. Right?
> 
Yes, the code also read the cache line. 
And prefetch to write helps writes. It saves snooping cost.

> >
> > With this change, 12.9% performance uplift was measured on N1SDP
> > platform with MLX5 NIC.
> >
> > Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> >
> > Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> 
> 
> On the octeontx2 platform, It is 2% regression.
> 
> Looks like micro architecture-specific item of handing write hint on the
> memory the area that does read and write.
> 
OK. Performance impact of the write hint may be different on various micro architecture implementations.
The 12% measured on N1 is not a small enough number to ignore. How about using a flag to distinguish prefetches invoked on different SoCs?
A compile time flag like RTE_USE_PREFETCH_WRITE is introduced. And SoCs enable it based on need.

> 
> I am testing the LPM lookup miss case.
> 
> My test command:
> ./build/examples/dpdk-l3fwd  -c 0x0100  -- -p 0x1 --config="(0,0,8)" -P
> 
> 
> 
> > ---
> >  examples/l3fwd/l3fwd_lpm_neon.h | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/examples/l3fwd/l3fwd_lpm_neon.h
> > b/examples/l3fwd/l3fwd_lpm_neon.h index d6c0ba64a..ae8840694 100644
> > --- a/examples/l3fwd/l3fwd_lpm_neon.h
> > +++ b/examples/l3fwd/l3fwd_lpm_neon.h
> > @@ -97,13 +97,13 @@ l3fwd_lpm_send_packets(int nb_rx, struct
> rte_mbuf
> > **pkts_burst,
> >
> >         if (k) {
> >                 for (i = 0; i < FWDSTEP; i++) {
> > -                       rte_prefetch0(rte_pktmbuf_mtod(pkts_burst[i],
> > +
> > + rte_prefetch0_write(rte_pktmbuf_mtod(pkts_burst[i],
> >                                                 struct rte_ether_hdr *) + 1);
> >                 }
> >
> >                 for (j = 0; j != k - FWDSTEP; j += FWDSTEP) {
> >                         for (i = 0; i < FWDSTEP; i++) {
> > -                               rte_prefetch0(rte_pktmbuf_mtod(
> > +                               rte_prefetch0_write(rte_pktmbuf_mtod(
> >                                                 pkts_burst[j + i + FWDSTEP],
> >                                                 struct rte_ether_hdr *) + 1);
> >                         }
> > @@ -124,17 +124,17 @@ l3fwd_lpm_send_packets(int nb_rx, struct
> rte_mbuf **pkts_burst,
> >                 /* Prefetch last up to 3 packets one by one */
> >                 switch (m) {
> >                 case 3:
> > -                       rte_prefetch0(rte_pktmbuf_mtod(pkts_burst[j],
> > +
> > + rte_prefetch0_write(rte_pktmbuf_mtod(pkts_burst[j],
> >                                                 struct rte_ether_hdr *) + 1);
> >                         j++;
> >                         /* fallthrough */
> >                 case 2:
> > -                       rte_prefetch0(rte_pktmbuf_mtod(pkts_burst[j],
> > +
> > + rte_prefetch0_write(rte_pktmbuf_mtod(pkts_burst[j],
> >                                                 struct rte_ether_hdr *) + 1);
> >                         j++;
> >                         /* fallthrough */
> >                 case 1:
> > -                       rte_prefetch0(rte_pktmbuf_mtod(pkts_burst[j],
> > +
> > + rte_prefetch0_write(rte_pktmbuf_mtod(pkts_burst[j],
> >                                                 struct rte_ether_hdr *) + 1);
> >                         j++;
> >                 }
> > --
> > 2.25.1
> >

  parent reply	other threads:[~2021-05-19  7:53 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-18 10:25 [dpdk-dev] [PATCH 0/4] l3fwd improvements Ruifeng Wang
2021-03-18 10:25 ` [dpdk-dev] [PATCH 1/4] examples/l3fwd: tune prefetch for better performance Ruifeng Wang
2021-04-13 18:50   ` Jerin Jacob
2021-04-13 20:00     ` Honnappa Nagarahalli
2021-05-19  7:52     ` Ruifeng Wang [this message]
2021-03-18 10:25 ` [dpdk-dev] [PATCH 2/4] examples/l3fwd: eliminate unnecessary calculations Ruifeng Wang
2021-04-13 18:40   ` Jerin Jacob
2021-03-18 10:25 ` [dpdk-dev] [PATCH 3/4] examples/l3fwd: eliminate unnecessary reloads in loop Ruifeng Wang
2021-04-13 17:43   ` Jerin Jacob
2021-04-14  6:02     ` Ruifeng Wang
2021-03-18 10:25 ` [dpdk-dev] [PATCH 4/4] examples/l3fwd: make data struct to be memory efficient Ruifeng Wang
2021-04-13 19:06   ` Jerin Jacob
2021-04-21  5:22     ` Hemant Agrawal
2021-04-26 10:55       ` Walsh, Conor
2021-04-27  1:19         ` Ruifeng Wang
2021-04-13  8:24 ` [dpdk-dev] [PATCH 0/4] l3fwd improvements Ruifeng Wang
2021-04-13 17:33   ` Jerin Jacob
2021-04-16  9:39 ` Ling, WeiX
2021-06-01  7:56 ` [dpdk-dev] [PATCH v2 0/3] " Ruifeng Wang
2021-06-01  7:56   ` [dpdk-dev] [PATCH v2 1/3] examples/l3fwd: reorganize code for better performance Ruifeng Wang
2021-06-06 18:34     ` Jerin Jacob
2021-06-01  7:56   ` [dpdk-dev] [PATCH v2 2/3] examples/l3fwd: eliminate unnecessary calculations Ruifeng Wang
2021-06-01  7:56   ` [dpdk-dev] [PATCH v2 3/3] examples/l3fwd: eliminate unnecessary reloads in loop Ruifeng Wang
2021-06-06 18:39     ` Jerin Jacob
2021-06-10  6:57 ` [dpdk-dev] [PATCH v3 0/2] l3fwd improvements Ruifeng Wang
2021-06-10  6:57   ` [dpdk-dev] [PATCH v3 1/2] examples/l3fwd: eliminate unnecessary calculations Ruifeng Wang
2021-06-10  6:57   ` [dpdk-dev] [PATCH v3 2/2] examples/l3fwd: eliminate unnecessary reloads in loop Ruifeng Wang
2021-07-05  8:36   ` [dpdk-dev] [PATCH v3 0/2] l3fwd improvements David Marchand

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