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From: Olivier Matz <olivier.matz@6wind.com>
To: Bruce Richardson <bruce.richardson@intel.com>
Cc: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [RFC 0/8] mbuf: structure reorganization
Date: Thu, 16 Feb 2017 17:14:10 +0100	[thread overview]
Message-ID: <20170216171410.57bff4ed@platinum> (raw)
In-Reply-To: <20170216154619.GA115208@bricha3-MOBL3.ger.corp.intel.com>

On Thu, 16 Feb 2017 15:46:19 +0000, Bruce Richardson
<bruce.richardson@intel.com> wrote:
> On Thu, Feb 16, 2017 at 02:48:07PM +0100, Olivier Matz wrote:
> > Hi Konstantin,
> > 
> > Thanks for the feedback.
> > Comments inline.
> > 
> > 
> > On Mon, 6 Feb 2017 18:41:27 +0000, "Ananyev, Konstantin"
> > <konstantin.ananyev@intel.com> wrote:  
> > > Hi Olivier,
> > > Looks good in general, some comments from me below.
> > > Thanks
> > > Konstantin
> > >   
> > > > 
> > > > The main changes are:
> > > > - reorder structure to increase vector performance on some
> > > > non-ia platforms.
> > > > - add a 64bits timestamp field in the 1st cache line    
> > > 
> > > Wonder why it deserves to be in first cache line?
> > > How it differs from seqn below (pure SW stuff right now).  
> > 
> > In case the timestamp is set from a NIC value, it is set in the Rx
> > path. So that's why I think it deserve to be located in the 1st
> > cache line.
> > 
> > As you said, the seqn is a pure sw stuff right: it is set in a lib,
> > not in a PMD rx path.
> >   
> > > > - m->next, m->nb_segs, and m->refcnt are always initialized for
> > > > mbufs in the pool, avoiding the need of setting m->next
> > > > (located in the 2nd cache line) in the Rx path for mono-segment
> > > > packets.
> > > > - change port and nb_segs to 16 bits    
> > > 
> > > Not that I am completely against it,
> > > but changing nb_segs to 16 bits seems like an overkill to me.
> > > I think we can keep and extra 8bits for something more useful in
> > > future.  
> > 
> > In my case, I use the m->next field to chain more than 256 segments
> > for L4 socket buffers. It also updates nb_seg that can overflow.
> > It's not a big issue since at the end, nb_seg is decremented for
> > each segment. On the other hand, if I enable some sanity checks on
> > mbufs, it complains because the number of segments is not equal to
> > nb_seg.
> > 
> > There is also another use case with fragmentation as discussed
> > recently: http://dpdk.org/dev/patchwork/patch/19819/
> > 
> > Of course, dealing with a long mbuf list is not that efficient,
> > but the application can maintain another structure to accelerate the
> > access to the middle/end of the list.
> > 
> > Finally, we have other ideas to get additional 8 bits if required in
> > the future, so I don't think it's really a problem.
> > 
> >   
> > >   
> > > > - move seqn in the 2nd cache line
> > > > 
> > > > Things discussed but not done in the patchset:
> > > > - move refcnt and nb_segs to the 2nd cache line: many drivers
> > > > sets them in the Rx path, so it could introduce a performance
> > > > regression, or    
> > > 
> > > I wonder can refcnt only be moved into the 2-nd cacheline?
> > > As I understand thanks to other change (from above) m->refcnt 
> > > will already be initialized, so RX code don't need to touch it.
> > > Though yes, it still would require changes in all PMDs.  
> > 
> > Yes, I agree, some fields could be moved in the 2nd cache line once
> > all PMDs stop to write them in RX path. I propose to issue some
> > guidelines to PMD maintainers at the same time the patchset is
> > pushed. Then we can consider changing it in a future version, in
> > case we need more room in the 1st mbuf cache line.
> >  
> 
> If we are changing things, we should really do all that now, rather
> than storing up future breaks to mbuf. Worst case, we should plan for
> it immediately after the release where we make these changes. Have two
> releases that break mbuf immediately after each other - and flagged as
> such, but keep it stable thereafter. I don't like having technical
> debt on mbuf just after we supposedly "fix" it.

I think there is no need to do this change now. And I don't feel good
with the idea of having a patchset that updates all the PMDs to remove
the access to a field because it moved to the 2nd cache line
(especially thinking about vector PMDs).

That's why I think the plan could be:
- push an updated version of this patchset quickly
- advertise to PMD maintainers "you don't need to set the m->next,
  m->refcnt, and m->nb_segs in the RX path, please update your drivers"
- later, if we need more room in the 1st cache line of the mbuf, we
  can move refcnt and nb_seg, probably without impacting the
  performance.


Olivier

  reply	other threads:[~2017-02-16 16:14 UTC|newest]

Thread overview: 155+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-24 15:19 Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 1/8] mbuf: make segment prefree function public Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 2/8] mbuf: make raw free " Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 3/8] mbuf: set mbuf fields while in pool Olivier Matz
2017-01-24 15:50   ` Bruce Richardson
2017-02-28 14:51     ` Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 4/8] net: don't touch mbuf next or nb segs on Rx Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 5/8] mbuf: make rearm data address naturally aligned Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 6/8] mbuf: use 2 bytes for port and nb segments Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 7/8] mbuf: move sequence number in second cache line Olivier Matz
2017-01-24 15:19 ` [dpdk-dev] [RFC 8/8] mbuf: add a timestamp field Olivier Matz
2017-01-24 15:59 ` [dpdk-dev] [RFC 0/8] mbuf: structure reorganization Bruce Richardson
2017-01-24 16:16   ` Olivier MATZ
2017-02-06 18:41 ` Ananyev, Konstantin
2017-02-09 16:20   ` Morten Brørup
2017-02-09 16:56     ` Ananyev, Konstantin
2017-02-16 13:48   ` Olivier Matz
2017-02-16 15:46     ` Bruce Richardson
2017-02-16 16:14       ` Olivier Matz [this message]
2017-02-21 14:20         ` Morten Brørup
2017-02-21 14:28           ` Bruce Richardson
2017-02-21 15:04           ` Olivier MATZ
2017-02-21 15:18             ` Bruce Richardson
2017-02-21 15:18             ` Morten Brørup
2017-02-19 19:04       ` Chilikin, Andrey
2017-02-21  9:53         ` Olivier MATZ
2017-02-16 17:26     ` Jan Blunck
2017-02-17 10:51       ` Olivier Matz
2017-02-17 12:49         ` Nélio Laranjeiro
2017-02-17 13:51           ` Jan Blunck
2017-02-18  5:48             ` Andrew Rybchenko
2017-02-17 13:38         ` Jan Blunck
2017-02-17 14:17           ` Olivier Matz
2017-02-17 18:42             ` Ananyev, Konstantin
2017-02-21  9:53               ` Olivier MATZ
2017-02-21 10:28                 ` Ananyev, Konstantin
2017-02-20  9:27             ` Jan Blunck
2017-02-21  9:54               ` Olivier MATZ
2017-02-21 16:12                 ` Jan Blunck
2017-02-21 16:38                   ` Bruce Richardson
2017-02-21 17:04                     ` Jan Blunck
2017-02-21 17:26                       ` Ananyev, Konstantin
2017-02-21 19:17                         ` Jan Blunck
2017-02-21 20:30                           ` Ananyev, Konstantin
2017-02-21 21:51                             ` Morten Brørup
2017-02-24 14:11                               ` Olivier Matz
2017-02-24 14:00                             ` Olivier Matz
2017-02-24 14:21                               ` Bruce Richardson
2017-02-28  8:55                               ` Jan Blunck
2017-02-28  9:05                                 ` Ananyev, Konstantin
2017-02-28  9:23                                   ` Olivier Matz
2017-02-28  9:33                                     ` Jan Blunck
2017-02-28 10:29                                     ` Ananyev, Konstantin
2017-02-28 10:50                                       ` Olivier Matz
2017-02-28 11:48                                         ` Ananyev, Konstantin
2017-02-28 12:28                                           ` Olivier Matz
2017-02-28 22:53                                             ` Ananyev, Konstantin
2017-03-02 16:46                                               ` Olivier Matz
2017-03-08 11:11                                                 ` Ananyev, Konstantin
2017-03-20  9:00                                                   ` Olivier Matz
2017-03-22 17:42                                                     ` Ananyev, Konstantin
2017-03-24  8:35                                                       ` Jerin Jacob
2017-03-24 13:35                                                         ` Olivier Matz
2017-02-28  9:25                                   ` Jan Blunck
2017-02-19 23:45     ` Ananyev, Konstantin
2017-02-21  9:22     ` Morten Brørup
2017-02-21  9:54       ` Olivier MATZ
2017-03-08  9:41 ` [dpdk-dev] [PATCH 0/9] " Olivier Matz
2017-03-08  9:41   ` [dpdk-dev] [PATCH 1/9] mbuf: make segment prefree function public Olivier Matz
2017-03-08  9:41   ` [dpdk-dev] [PATCH 2/9] mbuf: make raw free " Olivier Matz
2017-03-08  9:41   ` [dpdk-dev] [PATCH 3/9] mbuf: set mbuf fields while in pool Olivier Matz
2017-03-31 11:21     ` Bruce Richardson
2017-03-31 11:51       ` Ananyev, Konstantin
2017-03-08  9:41   ` [dpdk-dev] [PATCH 4/9] drivers/net: don't touch mbuf next or nb segs on Rx Olivier Matz
2017-03-08  9:41   ` [dpdk-dev] [PATCH 5/9] mbuf: make rearm data address naturally aligned Olivier Matz
2017-03-08  9:41   ` [dpdk-dev] [PATCH 6/9] mbuf: use 2 bytes for port and nb segments Olivier Matz
2017-03-08  9:41   ` [dpdk-dev] [PATCH 7/9] mbuf: move sequence number in second cache line Olivier Matz
2017-03-08  9:42   ` [dpdk-dev] [PATCH 8/9] mbuf: add a timestamp field Olivier Matz
2017-04-04 10:29     ` [dpdk-dev] [PATCH 0/2] reduce writes to mbuf in ixgbe vRX Konstantin Ananyev
2017-04-07 15:13       ` Ferruh Yigit
2017-04-07 15:44         ` Ferruh Yigit
2017-04-09 22:56           ` Ananyev, Konstantin
2017-04-04 10:29     ` [dpdk-dev] [PATCH 1/2] net/ixgbe: eliminate mbuf write on rearm Konstantin Ananyev
2017-04-10 15:59       ` [dpdk-dev] [PATCH v2 0/2] reduce writes to mbuf in ixgbe vRX Konstantin Ananyev
2017-04-10 16:17         ` Ferruh Yigit
2017-04-10 15:59       ` [dpdk-dev] [PATCH v2 1/2] net/ixgbe: eliminate mbuf write on rearm Konstantin Ananyev
2017-04-10 15:59       ` [dpdk-dev] [PATCH v2 2/2] net/ixgbe: remove option to disable offload flags Konstantin Ananyev
2017-04-04 10:29     ` [dpdk-dev] [PATCH " Konstantin Ananyev
2017-03-08  9:42   ` [dpdk-dev] [PATCH 9/9] mbuf: reorder VLAN tci and buffer len fields Olivier Matz
2017-03-29 15:56   ` [dpdk-dev] [PATCH 0/9] mbuf: structure reorganization Olivier Matz
2017-03-29 16:03     ` Morten Brørup
2017-03-29 20:09     ` Bruce Richardson
2017-03-30  9:31       ` Bruce Richardson
2017-03-30 12:02         ` Olivier Matz
2017-03-30 12:23           ` Bruce Richardson
2017-03-30 16:45             ` Ananyev, Konstantin
2017-03-30 16:47               ` Ananyev, Konstantin
2017-03-30 18:06                 ` Ananyev, Konstantin
2017-03-31  8:41                   ` Olivier Matz
2017-03-31  9:58                     ` Ananyev, Konstantin
2017-03-31  1:00                 ` Ananyev, Konstantin
2017-03-31  7:21                   ` Morten Brørup
2017-03-31  8:26                   ` Olivier Matz
2017-03-31  8:41                     ` Bruce Richardson
2017-03-31  8:59                       ` Olivier Matz
2017-03-31  9:18                         ` Ananyev, Konstantin
2017-03-31  9:36                           ` Olivier Matz
2017-04-03 16:15                           ` Thomas Monjalon
2017-04-04  7:58                             ` Olivier MATZ
2017-04-04  8:53                               ` Bruce Richardson
2017-03-31  9:23                         ` Bruce Richardson
2017-03-31 11:18     ` Nélio Laranjeiro
2017-03-30 14:54   ` Andrew Rybchenko
2017-03-30 15:12   ` Jerin Jacob
2017-04-04 16:27   ` [dpdk-dev] [PATCH v2 0/8] " Olivier Matz
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 1/8] mbuf: make segment prefree function public Olivier Matz
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 2/8] mbuf: make raw free " Olivier Matz
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 3/8] mbuf: set mbuf fields while in pool Olivier Matz
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 4/8] drivers/net: don't touch mbuf next or nb segs on Rx Olivier Matz
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 5/8] mbuf: make rearm data address naturally aligned Olivier Matz
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port and nb segments Olivier Matz
2017-04-06  5:45       ` Yuanhan Liu
2017-04-18 13:03         ` Olivier MATZ
2017-07-04  7:54           ` Wang, Zhihong
2017-07-10  8:00             ` Olivier Matz
2017-07-10  8:15               ` Morten Brørup
2017-07-11 13:25                 ` Wiles, Keith
2017-07-11 13:30                   ` Morten Brørup
2017-07-11 15:05                     ` Thomas Monjalon
2017-07-11 15:23                       ` [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port and nbsegments Morten Brørup
2017-07-11 16:48                         ` Wiles, Keith
2017-07-12  7:25                           ` Morten Brørup
2017-07-12  9:02                             ` Yang, Zhiyong
2017-07-12  9:50                               ` [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port andnbsegments Morten Brørup
2017-07-12 15:35                                 ` Stephen Hemminger
2017-07-12 15:57                                   ` Morten Brørup
2017-07-12 16:23                                     ` Thomas Monjalon
2017-07-12 18:20                                       ` Wiles, Keith
2017-07-21 15:03                                       ` Bruce Richardson
2017-07-12 15:34                             ` [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port and nbsegments Wiles, Keith
2017-07-11 13:34                 ` [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port and nb segments Wiles, Keith
2017-07-11 13:46                   ` Olivier MATZ
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 7/8] mbuf: move sequence number in second cache line Olivier Matz
2017-04-04 16:28     ` [dpdk-dev] [PATCH v2 8/8] mbuf: add a timestamp field Olivier Matz
2017-04-05  9:37     ` [dpdk-dev] [PATCH v2 0/8] mbuf: structure reorganization Thomas Monjalon
2017-04-05  9:46       ` Olivier MATZ
2017-04-05  9:48       ` Richardson, Bruce
2017-04-05 12:06       ` Ferruh Yigit
2017-04-14 13:10       ` Ferruh Yigit
2017-04-18 13:04         ` Olivier MATZ
2017-04-19  9:39           ` Thomas Monjalon
2017-04-19 12:28             ` Olivier MATZ
2017-04-19 12:56               ` Thomas Monjalon
2017-04-19 13:03                 ` Ferruh Yigit
2017-04-19 13:12                   ` Thomas Monjalon

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