From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yongseok Koh Subject: Re: [PATCH v3 1/2] mbuf: support attaching external buffer to mbuf Date: Wed, 25 Apr 2018 09:44:17 -0700 Message-ID: <20180425164416.GA3268@yongseok-MBP.local> References: <20180310012532.15809-1-yskoh@mellanox.com> <20180419011105.9694-1-yskoh@mellanox.com> <2601191342CEEE43887BDE71AB977258AE91994F@IRSMSX102.ger.corp.intel.com> <20180424020427.GA83470@yongseok-MBP.local> <2601191342CEEE43887BDE71AB977258AEBCF960@IRSMSX102.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Lu, Wenzhuo" , "Wu, Jingjing" , "olivier.matz@6wind.com" , "dev@dpdk.org" , "adrien.mazarguil@6wind.com" , "nelio.laranjeiro@6wind.com" To: "Ananyev, Konstantin" Return-path: Received: from EUR01-VE1-obe.outbound.protection.outlook.com (mail-ve1eur01on0053.outbound.protection.outlook.com [104.47.1.53]) by dpdk.org (Postfix) with ESMTP id A2B1E8DF0 for ; Wed, 25 Apr 2018 18:44:36 +0200 (CEST) Content-Disposition: inline In-Reply-To: <2601191342CEEE43887BDE71AB977258AEBCF960@IRSMSX102.ger.corp.intel.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Wed, Apr 25, 2018 at 01:16:38PM +0000, Ananyev, Konstantin wrote: > > > > > > On Mon, Apr 23, 2018 at 11:53:04AM +0000, Ananyev, Konstantin wrote: > > [...] > > > > @@ -693,9 +711,14 @@ rte_mbuf_to_baddr(struct rte_mbuf *md) > > > > #define RTE_MBUF_INDIRECT(mb) ((mb)->ol_flags & IND_ATTACHED_MBUF) > > > > > > > > /** > > > > + * Returns TRUE if given mbuf has external buffer, or FALSE otherwise. > > > > + */ > > > > +#define RTE_MBUF_HAS_EXTBUF(mb) ((mb)->ol_flags & EXT_ATTACHED_MBUF) > > > > + > > > > +/** > > > > * Returns TRUE if given mbuf is direct, or FALSE otherwise. > > > > */ > > > > -#define RTE_MBUF_DIRECT(mb) (!RTE_MBUF_INDIRECT(mb)) > > > > +#define RTE_MBUF_DIRECT(mb) (!RTE_MBUF_INDIRECT(mb) && !RTE_MBUF_HAS_EXTBUF(mb)) > > > > > > As a nit: > > > RTE_MBUF_DIRECT(mb) (((mb)->ol_flags & (IND_ATTACHED_MBUF | EXT_ATTACHED_MBUF)) == 0) > > > > It was for better readability and I expected compiler did the same. > > But, if you still want this way, I can change it. > > I know compilers are quite smart these days, but you never know for sure, > so yes, I think better to do that explicitly. Okay. > > [...] > > > > /** > > > > - * Detach an indirect packet mbuf. > > > > + * @internal used by rte_pktmbuf_detach(). > > > > + * > > > > + * Decrement the reference counter of the external buffer. When the > > > > + * reference counter becomes 0, the buffer is freed by pre-registered > > > > + * callback. > > > > + */ > > > > +static inline void > > > > +__rte_pktmbuf_free_extbuf(struct rte_mbuf *m) > > > > +{ > > > > + struct rte_mbuf_ext_shared_info *shinfo; > > > > + > > > > + RTE_ASSERT(RTE_MBUF_HAS_EXTBUF(m)); > > > > + > > > > + shinfo = rte_mbuf_ext_shinfo(m); > > > > + > > > > + if (rte_extbuf_refcnt_update(shinfo, -1) == 0) > > > > + shinfo->free_cb(m->buf_addr, shinfo->fcb_opaque); > > > > > > > > > I understand the reason but extra function call for each external mbuf - seems quite expensive. > > > Wonder is it possible to group them somehow and amortize the cost? > > > > Good point. I thought about it today. > > > > Comparing to the regular mbuf, maybe three differences. a) free function isn't > > inlined but a real branch. b) no help from core local cache like mempool's c) no > > free_bulk func like rte_mempool_put_bulk(). But these look quite costly and > > complicated for the external buffer attachment. > > > > For example, to free it in bulk, external buffers should be grouped as the > > buffers would have different callback functions. To do that, I have to make an > > API to pre-register an external buffer group to prepare resources for the bulk > > free. Then, buffers can't be anonymous anymore but have to be registered in > > advance. If so, it would be better to use existing APIs, especially when a user > > wants high throughput... > > > > Let me know if you have better idea to implement it. Then, I'll gladly take > > that. Or, we can push any improvement patch in the next releases. > > I don't have any extra-smart thoughts here. > One option I thought about - was to introduce group of external buffers with > common free routine (I think o mentioned it already). > Second - hide all that external buffer management inside mempool, > i.e. if user wants to use external buffers he create a mempool > (with rte_mbuf_ext_shared_info as elements?), then attach external buffer to shinfo > and call mbuf_attach_external(mbuf, shinfo). > Though for free we can just call mempool_put(shinfo) and let particular implementation > decide when/how call free_cb(), etc. I don't want to restrict external buffer to mempool object. Especially for storage users, they want to use **any** buffer, even coming outside of DPDK. However, will open a follow-up discussion for this in the next release window probably with more measurement data. Thank you for suggestions. Yongseok