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From: "Richardson, Bruce" <bruce.richardson@intel.com>
To: Neil Horman <nhorman@tuxdriver.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field
Date: Wed, 17 Sep 2014 16:02:07 +0000
Message-ID: <59AF69C657FD0841A61C55336867B5B0343F2F91@IRSMSX103.ger.corp.intel.com> (raw)
In-Reply-To: <20140917153510.GG4213@localhost.localdomain>

> -----Original Message-----
> From: Neil Horman [mailto:nhorman@tuxdriver.com]
> Sent: Wednesday, September 17, 2014 4:35 PM
> To: Richardson, Bruce
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field
> 
> On Wed, Sep 17, 2014 at 11:01:41AM +0100, Bruce Richardson wrote:
> > While some applications may store metadata about packets in the packet
> > mbuf headroom, this is not a workable solution for packet metadata which
> > is either:
> > * larger than the headroom (or headroom is needed for adding pkt headers)
> > * needs to be shared or copied among packets
> >
> > To support these use cases in applications, we reserve a general
> > "userdata" pointer field inside the second cache-line of the mbuf. This
> > is better than having the application store the pointer to the external
> > metadata in the packet headroom, as it saves an additional cache-line
> > from being used.
> >
> > Apart from storing metadata, this field also provides a general 8-byte
> > scratch space inside the mbuf for any other application uses that are
> > applicable.
> >
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> >  lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h | 3 ++-
> >  lib/librte_mbuf/rte_mbuf.h                                    | 3 +++
> >  2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> > index 25ed672..d27e891 100644
> > --- a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> > +++ b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> > @@ -117,7 +117,8 @@ struct rte_kni_mbuf {
> >  	uint16_t data_len;      /**< Amount of data in segment buffer. */
> >  	uint32_t pkt_len;       /**< Total pkt len: sum of all segment data_len. */
> >  	char pad3[8];
> > -	void *pool __attribute__((__aligned__(64)));
> > +	void *pad4 __attribute__((__aligned__(64)));
> > +	void *pool;
> I don't see a comment about this in the changelog, only about the userdata
> pointer being added below.

Yes, this is the userdata pointer - just added as padding here, since it's not actually needed by the kernel-side KNI module.

> 
> 
> >  	void *next;
> >  };
> >
> > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > index 8e27d2e..b1acfc3 100644
> > --- a/lib/librte_mbuf/rte_mbuf.h
> > +++ b/lib/librte_mbuf/rte_mbuf.h
> > @@ -172,6 +172,9 @@ struct rte_mbuf {
> >
> >  	/* second cache line - fields only used in slow path or on TX */
> >  	MARKER cacheline1 __rte_cache_aligned;
> > +
> > +	void *userdata;           /**< Can be used for external metadata */
> > +
> Do you want to make this a void* or a char[8]?  I ask because if people are
> going to use is as a scratch space (rather than a pointer), they get a suprise
> when they build this on 32 bit systems, and their 8 byte scratch space is
> reduced to 4 bytes.

I think this is better as a pointer, as that is how it is likely to be used. As for 32-bit, I'm torn between wanting to just update the comment and feeling the need to update the code to actually make the thing 8-byte on 32-bit! Changing the comment to be more accurate is easier, unions are ugly looking in the structure IMHO, so maybe I'll just mark the following field (pool) as always 8-byte aligned....

/Bruce

> 
> Neil
> 
> >  	struct rte_mempool *pool; /**< Pool from which mbuf was allocated.
> */
> >  	struct rte_mbuf *next;    /**< Next segment of scattered packet. */
> >
> > --
> > 1.9.3
> >
> >

  reply	other threads:[~2014-09-17 15:59 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-17 10:01 [dpdk-dev] [PATCH 0/5] Mbuf Structure Rework, part 3 Bruce Richardson
2014-09-17 10:01 ` [dpdk-dev] [PATCH 1/5] mbuf: ensure next pointer is set to null on free Bruce Richardson
2014-09-17 10:01 ` [dpdk-dev] [PATCH 2/5] ixgbe: add prefetch to improve slow-path tx perf Bruce Richardson
2014-09-17 15:21   ` Neil Horman
2014-09-17 15:35     ` Richardson, Bruce
2014-09-17 17:59       ` Neil Horman
2014-09-18 13:36         ` Bruce Richardson
2014-09-18 15:29           ` Neil Horman
2014-09-18 15:42             ` Bruce Richardson
2014-09-18 17:56               ` Neil Horman
2014-09-17 10:01 ` [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32 Bruce Richardson
2014-09-17 15:29   ` Neil Horman
2014-09-18 15:53     ` Richardson, Bruce
2014-09-18 17:13       ` Thomas Monjalon
2014-09-18 18:08         ` Neil Horman
2014-09-19  9:18           ` Richardson, Bruce
2014-09-19 10:24             ` Neil Horman
2014-09-19 10:28               ` Richardson, Bruce
2014-09-19 15:18                 ` Neil Horman
2014-09-18 18:03       ` Neil Horman
2014-09-17 10:01 ` [dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field Bruce Richardson
2014-09-17 15:35   ` Neil Horman
2014-09-17 16:02     ` Richardson, Bruce [this message]
2014-09-17 18:29       ` Neil Horman
2014-09-17 10:01 ` [dpdk-dev] [PATCH 5/5] mbuf: Add in second vlan tag field to mbuf Bruce Richardson
2014-09-17 20:46   ` Stephen Hemminger
2014-09-23 11:08 ` [dpdk-dev] [PATCH v2 0/5] Mbuf Structure Rework, part 3 Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 1/5] mbuf: ensure next pointer is set to null on free Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 2/5] ixgbe: add prefetch to improve slow-path tx perf Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 3/5] testpmd: Change rxfreet default to 32 Bruce Richardson
2014-09-23 17:02     ` Neil Horman
2014-09-24  9:03       ` Richardson, Bruce
2014-09-24 10:05         ` Neil Horman
2014-11-07 12:30         ` Thomas Monjalon
2014-11-07 13:49           ` Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 4/5] mbuf: add userdata pointer field Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 5/5] mbuf: switch vlan_tci and reserved2 fields Bruce Richardson
2014-09-29 15:58   ` [dpdk-dev] [PATCH v2 0/5] Mbuf Structure Rework, part 3 De Lara Guarch, Pablo
2014-10-08 12:31     ` Thomas Monjalon

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