Hi Konstantin, > -----Original Message----- > From: Ananyev, Konstantin > Sent: Monday, May 29, 2017 8:52 PM > To: Hu, Jiayu <jiayu...@intel.com> > Cc: dev@dpdk.org; Wiles, Keith <keith.wi...@intel.com>; > yuanhan....@linux.intel.com > Subject: RE: [PATCH v3 1/3] lib: add Generic Receive Offload API framework > > Hi Jiayu, > > > -----Original Message----- > > From: Hu, Jiayu > > Sent: Monday, May 29, 2017 11:23 AM > > To: Ananyev, Konstantin <konstantin.anan...@intel.com> > > Cc: dev@dpdk.org; Wiles, Keith <keith.wi...@intel.com>; > yuanhan....@linux.intel.com > > Subject: RE: [PATCH v3 1/3] lib: add Generic Receive Offload API > framework > > > > Hi Konstantin, > > > > > -----Original Message----- > > > From: Ananyev, Konstantin > > > Sent: Sunday, May 28, 2017 12:51 AM > > > To: Hu, Jiayu <jiayu...@intel.com> > > > Cc: dev@dpdk.org; Wiles, Keith <keith.wi...@intel.com>; > > > yuanhan....@linux.intel.com > > > Subject: RE: [PATCH v3 1/3] lib: add Generic Receive Offload API > framework > > > > > > > > > Hi Jiayu, > > > > > > > > > > > Hi Konstantin, > > > > > > > > On Sat, May 27, 2017 at 07:12:16PM +0800, Ananyev, Konstantin wrote: > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > From: Hu, Jiayu > > > > > > Sent: Saturday, May 27, 2017 4:42 AM > > > > > > To: Ananyev, Konstantin <konstantin.anan...@intel.com> > > > > > > Cc: dev@dpdk.org; Wiles, Keith <keith.wi...@intel.com>; > > > yuanhan....@linux.intel.com > > > > > > Subject: Re: [PATCH v3 1/3] lib: add Generic Receive Offload API > > > framework > > > > > > > > > > > > On Sat, May 27, 2017 at 07:10:21AM +0800, Ananyev, Konstantin > wrote: > > > > > > > Hi Jiayu, > > > > > > > > > > > > > > > -----Original Message----- > > > > > > > > From: Hu, Jiayu > > > > > > > > Sent: Friday, May 26, 2017 8:26 AM > > > > > > > > To: Ananyev, Konstantin <konstantin.anan...@intel.com> > > > > > > > > Cc: dev@dpdk.org; Wiles, Keith <keith.wi...@intel.com>; > > > yuanhan....@linux.intel.com > > > > > > > > Subject: Re: [PATCH v3 1/3] lib: add Generic Receive Offload API > > > framework > > > > > > > > > > > > > > > > Hi Konstantin, > > > > > > > > > > > > > > > > On Wed, May 24, 2017 at 08:38:25PM +0800, Ananyev, > Konstantin > > > wrote: > > > > > > > > > > > > > > > > > > Hi Jiayu, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi Konstantin, > > > > > > > > > > > > > > > > > > > > Thanks for your comments. My replies/questions are below. > > > > > > > > > > > > > > > > > > > > BRs, > > > > > > > > > > Jiayu > > > > > > > > > > > > > > > > > > > > On Mon, May 22, 2017 at 05:19:19PM +0800, Ananyev, > > > Konstantin wrote: > > > > > > > > > > > Hi Jiayu, > > > > > > > > > > > My comments/questions below. > > > > > > > > > > > Konstantin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > For applications, DPDK GRO provides three external > functions > > > to > > > > > > > > > > > > enable/disable GRO: > > > > > > > > > > > > - rte_gro_init: initialize GRO environment; > > > > > > > > > > > > - rte_gro_enable: enable GRO for a given port; > > > > > > > > > > > > - rte_gro_disable: disable GRO for a given port. > > > > > > > > > > > > Before using GRO, applications should explicitly call > > > rte_gro_init to > > > > > > > > > > > > initizalize GRO environment. After that, applications > > > > > > > > > > > > can > call > > > > > > > > > > > > rte_gro_enable to enable GRO and call rte_gro_disable > to > > > disable GRO for > > > > > > > > > > > > specific ports. > > > > > > > > > > > > > > > > > > > > > > I think this is too restrictive and wouldn't meet various > user's > > > needs. > > > > > > > > > > > User might want to: > > > > > > > > > > > - enable/disable GRO for particular RX queue > > > > > > > > > > > - or even setup different GRO types for different RX > > > > > > > > > > > queues, > > > > > > > > > > > i.e, - GRO over IPV4/TCP for queue 0, and GRO over > > > IPV6/TCP for queue 1, etc. > > > > > > > > > > > > > > > > > > > > The reason for enabling/disabling GRO per-port instead of > per- > > > queue is that LINUX > > > > > > > > > > controls GRO per-port. To control GRO per-queue indeed can > > > provide more flexibility > > > > > > > > > > to applications. But are there any scenarios that different > > > queues of a port may > > > > > > > > > > require different GRO control (i.e. GRO types and > enable/disable > > > GRO)? > > > > > > > > > > > > > > > > > > I think yes. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - For various reasons, user might prefer not to use RX > callbacks > > > for various reasons, > > > > > > > > > > > But invoke gro() manually at somepoint in his code. > > > > > > > > > > > > > > > > > > > > An application-used GRO library can enable more flexibility > > > > > > > > > > to > > > applications. Besides, > > > > > > > > > > when perform GRO in ethdev layer or inside PMD drivers, it > > > > > > > > > > is > an > > > issue that > > > > > > > > > > rte_eth_rx_burst returns actually received packet number or > > > GROed packet number. And > > > > > > > > > > the same issue happens in GSO, and even more seriously. > This is > > > because applications > > > > > > > > > > , like VPP, always rely on the return value of > > > > > > > > > > rte_eth_tx_burst > to > > > decide further > > > > > > > > > > operations. If applications can direcly call GRO/GSO > > > > > > > > > > libraries, > > > this issue won't exist. > > > > > > > > > > And DPDK is a library, which is not a holistic system like > LINUX. > > > We don't need to do > > > > > > > > > > the same as LINUX. Therefore, maybe it's a better idea to > > > directly provide SW > > > > > > > > > > segmentation/reassembling libraries to applications. > > > > > > > > > > > > > > > > > > > > > - Many users would like to control size (number of > flows/items > > > per flow), > > > > > > > > > > > max allowed packet size, max timeout, etc., for > > > > > > > > > > > different > GRO > > > tables. > > > > > > > > > > > - User would need a way to flush all or only timeout > packets > > > from particular GRO tables. > > > > > > > > > > > > > > > > > > > > > > So I think that API needs to extended to become be much > more > > > fine-grained. > > > > > > > > > > > Something like that: > > > > > > > > > > > > > > > > > > > > > > struct rte_gro_tbl_param { > > > > > > > > > > > int32_t socket_id; > > > > > > > > > > > size_t max_flows; > > > > > > > > > > > size_t max_items_per_flow; > > > > > > > > > > > size_t max_pkt_size; > > > > > > > > > > > uint64_t packet_timeout_cycles; > > > > > > > > > > > <desired GRO types (IPV4_TCP | IPV6_TCP, ...)> > > > > > > > > > > > <probably type specific params> > > > > > > > > > > > ... > > > > > > > > > > > }; > > > > > > > > > > > > > > > > > > > > > > struct rte_gro_tbl; > > > > > > > > > > > strct rte_gro_tbl *rte_gro_tbl_create(const struct > > > rte_gro_tbl_param *param); > > > > > > > > > > > > > > > > > > > > > > void rte_gro_tbl_destroy(struct rte_gro_tbl *tbl); > > > > > > > > > > > > > > > > > > > > Yes, I agree with you. It's necessary to provide more fine- > > > grained control APIs to > > > > > > > > > > applications. But what's 'packet_timeout_cycles' used for? > > > > > > > > > > Is > it > > > for TCP packets? > > > > > > > > > > > > > > > > > > For any packets that sits in the gro_table for too long. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* > > > > > > > > > > > * process packets, might store some packets inside the > GRO > > > table, > > > > > > > > > > > * returns number of filled entries in pkt[] > > > > > > > > > > > */ > > > > > > > > > > > uint32_t rte_gro_tbl_process(struct rte_gro_tbl *tbl, > > > > > > > > > > > struct > > > rte_mbuf *pkt[], uint32_t num); > > > > > > > > > > > > > > > > > > > > > > /* > > > > > > > > > > > * retirieves up to num timeouted packets from the table. > > > > > > > > > > > */ > > > > > > > > > > > uint32_t rtre_gro_tbl_timeout(struct rte_gro_tbl *tbl, > uint64_t > > > tmt, struct rte_mbuf *pkt[], uint32_t num); > > > > > > > > > > > > > > > > > > > > Currently, we implement GRO as RX callback, whose > processing > > > logic is simple: > > > > > > > > > > receive burst packets -> perform GRO -> return to > > > > > > > > > > application. > > > GRO stops after > > > > > > > > > > finishing processing received packets. If we provide > > > rte_gro_tbl_timeout, when > > > > > > > > > > and who will call it? > > > > > > > > > > > > > > > > > > I mean the following scenario: > > > > > > > > > We receive a packet, find it is eligible for GRO and put it > > > > > > > > > into > > > gro_table > > > > > > > > > in expectation - there would be more packets for the same > flow. > > > > > > > > > But it could happen that we would never (or for some long > time) > > > receive > > > > > > > > > any new packets for that flow. > > > > > > > > > So the first packet would never be delivered to the upper > > > > > > > > > layer, > > > > > > > > > or delivered too late. > > > > > > > > > So we need a mechanism to extract such not merged packets > > > > > > > > > and push them to the upper layer. > > > > > > > > > My thought it would be application responsibility to call it > > > > > > > > > from > > > time to time. > > > > > > > > > That's actually another reason why I think we shouldn't use > > > application > > > > > > > > > to always use RX callbacks for GRO. > > > > > > > > > > > > > > > > Currently, we only provide one reassembly function, > > > rte_gro_reassemble_burst, > > > > > > > > which merges N inputted packets at a time. After finishing > > > processing these > > > > > > > > packets, it returns all of them and reset hashing tables. > Therefore, > > > there > > > > > > > > are no packets in hashing tables after rte_gro_reassemble_burst > > > returns. > > > > > > > > > > > > > > Ok, sorry I missed that part with rte_hash_reset(). > > > > > > > So gro_ressemble_burst() performs only inline processing on > current > > > input packets > > > > > > > and doesn't try to save packets for future merging, correct? > > > > > > > > > > > > Yes. > > > > > > > > > > > > > Such approach indeed is much lightweight and doesn't require any > > > extra timeouts and flush(). > > > > > > > So my opinion let's keep it like that - nice and simple. > > > > > > > BTW, I think in that case we don't need any hashtables (or any > other > > > persistent strucures)at all. > > > > > > > What we need is just a set of GROs (tcp4, tpc6, etc.) we want to > > > perform on given array of packets. > > > > > > > > > > > > Beside GRO types that are desired to perform, maybe it also needs > > > max_pkt_size and > > > > > > some GRO type specific information? > > > > > > > > > > Yes, but we don't need the actual hash-tables, etc. inside. > > > > > Passing something like struct gro_param seems enough. > > > > > > > > Yes, we can just pass gro_param and allocate hashing tables > > > > inside rte_gro_reassemble_burst. If so, hashing tables of > > > > desired GRO types are created and freed in each invocation > > > > of rte_gro_reassemble_burst. In GRO library, hashing tables > > > > are created by GRO type specific gro_tbl_create_fn. These > > > > gro_tbl_create_fn may allocate hashing table space via malloc > > > > (or rte_malloc). Therefore, we may frequently call malloc/free > > > > when using rte_gro_reassemble_burst. In my opinion, it will > > > > degrade GRO performance greatly. > > > > > > I don't' understand why do we need to put/extract each packet into/from > > > hash table at all. > > > We have N input packets that need to be grouped/sorted by some > criteria. > > > Surely that can be done without any hash-table involved. > > > What is the need for hash table and all the overhead it brings here? > > > > In current design, I assume all GRO types use hash tables to merge > > packets. The key of the hash table is the criteria to merge packets. > > So the main difference for different GRO types' hash tables is the > > key definition. > > > > And the reason for using hash tables is to speed up reassembly. Given > > There are N TCP packets inputted, the simplest way to process packets[i] > > Is to traverse processed packets[0]~packets[i-1] and try to find a one > > to merge. In the worst case, we need to check all of packets[0~i-1]. > > In this case, the time complexity of processing N packets is O(N^2). > > If we use a hash table, whose key is the criteria to merge two packets, > > the time to find a packet that may be merged with packets[i] is O(1). > > I understand that, but add/search inside the hash table, > plus resetting it for every burst of packets doesn't come for free also. > I think that for most common burst sizes (< 100 packets) > hash overhead would significantly overweight the price of > worst case O(N^2) scan.
Yes, the packet burst size is always less than 100, which may amplify the cost of using hash tables. To avoid the high price, maybe a simpler structure, like rte_ip_frag_tbl in IP reassembly library, is better. And actually, I have never tried other designs. In next version, I will use a simpler structure to merge TCP packets and compare performance results. Thanks. > Also, if such worst case really worries you, you can pre-sort > input packets first before starting the actual reassemble for them. If the inputted N packets are consist of N1 TCP packets and N2 UDP packets. If we pre-sort them, what should they look like after sorting? > That might help to bring the price down. > Konstantin Jiayu > > > > > Do you think it's too complicated? > > > > Jiayu > > > > > Konstantin > > > > > > > > > > > But if we ask applications to input hashing tables, what we > > > > need to do is to reset them after finishing using in > > > > rte_gro_reassemble_burst, rather than to malloc and free each > > > > time. Therefore, I think this way is more efficient. How do you > > > > think? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > If we provide rte_gro_tbl_timeout, we also need to provide > another > > > reassmebly > > > > > > > > function, like rte_gro_reassemble, which processes one given > > > packet at a > > > > > > > > time and won't reset hashing tables. Applications decide when to > > > flush packets > > > > > > > > in hashing tables. And rte_gro_tbl_timeout is one of the ways > that > > > can be used > > > > > > > > to flush the packets. Do you mean that? > > > > > > > > > > > > > > Yes, that's what I meant, but as I said above - I think your > approach is > > > probably > > > > > > > more preferable - it is much simpler and lightweight. > > > > > > > Konstantin > > > > > > >