From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.tuxdriver.com (charlotte.tuxdriver.com [70.61.120.58]) by dpdk.org (Postfix) with ESMTP id A5FF3B39C for ; Wed, 17 Sep 2014 20:24:21 +0200 (CEST) Received: from hmsreliant.think-freely.org ([2001:470:8:a08:7aac:c0ff:fec2:933b] helo=localhost) by smtp.tuxdriver.com with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.63) (envelope-from ) id 1XUJzD-0002go-Vd; Wed, 17 Sep 2014 14:29:58 -0400 Date: Wed, 17 Sep 2014 14:29:51 -0400 From: Neil Horman To: "Richardson, Bruce" Message-ID: <20140917182951.GB13492@hmsreliant.think-freely.org> References: <1410948102-12740-1-git-send-email-bruce.richardson@intel.com> <1410948102-12740-5-git-send-email-bruce.richardson@intel.com> <20140917153510.GG4213@localhost.localdomain> <59AF69C657FD0841A61C55336867B5B0343F2F91@IRSMSX103.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <59AF69C657FD0841A61C55336867B5B0343F2F91@IRSMSX103.ger.corp.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Score: -2.9 (--) X-Spam-Status: No Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 17 Sep 2014 18:24:22 -0000 On Wed, Sep 17, 2014 at 04:02:07PM +0000, Richardson, Bruce wrote: > > -----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 > > > --- > > > 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 > > > > > > >