[dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field
> -Original Message- > From: Neil Horman [mailto:nhorman at tuxdriver.com] > Sent: Wednesday, September 17, 2014 4:35 PM > To: Richardson, Bruce > Cc: dev at 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 > > --- > > 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 > > > >
[dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field
On Wed, Sep 17, 2014 at 04:02:07PM +, Richardson, Bruce wrote: > > -Original Message- > > From: Neil Horman [mailto:nhorman at tuxdriver.com] > > Sent: Wednesday, September 17, 2014 4:35 PM > > To: Richardson, Bruce > > Cc: dev at 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 > > > --- > > > 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. > Ah, then maybe merge it with the pad3 pointer, to make it look a bit better? > > > > > > > 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 > Ok, however you want to bring it into alignment, as long as its clear that its either 8 bytes always, or a variable size based on the arch. Best Neil > /Bruce > > > > > Neil > > > > > struct rte_mempool *pool; /**< Pool from which mbuf was allocated. > > */ > > > struct rte_mbuf *next;/**< Next segment of scattered packet. */ > > > > > > -- > > > 1.9.3 > > > > > > >
[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 > --- > 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. > 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. Neil > struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */ > struct rte_mbuf *next;/**< Next segment of scattered packet. */ > > -- > 1.9.3 > >
[dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field
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 --- 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; 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 */ + struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */ struct rte_mbuf *next;/**< Next segment of scattered packet. */ -- 1.9.3