Date: Mon, 27 Nov 2017 09:33:06 +0100 From: Vincenzo Maffione <v.maffione@gmail.com> To: Xiaoye Sun <Xiaoye.Sun@rice.edu> Cc: Luigi Rizzo <rizzo@iet.unipi.it>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Victor Detoni <victordetoni@gmail.com>, Pavel Odintsov <pavel.odintsov@gmail.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it> Subject: Re: swaping ring slots between NIC ring and Host ring does not always success Message-ID: <CA%2B_eA9jHT_R5id2kZBMe_j-Lc0-%2BvXuX4e8bqvy1cXymvaQN-A@mail.gmail.com> In-Reply-To: <CAJnByziVfVJ6gX_aL%2BwFvmW9ZsfwPV1RRCkxgEbZMoe1kSo35A@mail.gmail.com> References: <CAJnByzj6Dj3vouZ2NbxqvCV-2-7TVtTR4FaWKuCFaaRN2X%2ByAA@mail.gmail.com> <CALgsdbd3XuE3wMYp4ey%2B1aer%2BHSVNojLYoVqwqTBPAXXdf9i%2BQ@mail.gmail.com> <CAJnByzirLXdCe-kwHV2s_E6ytGJG0Dth=0Ms12RrEk7FK_%2B8Og@mail.gmail.com> <CA%2BhQ2%2BgMWY0eabjHGw0=PJCAkS-wO=RBrN5brSbaqWc3_AOYoQ@mail.gmail.com> <CAJnByziBS8o6LtmpUrUu5xtRUd008Z2hnCsp=WVFv35r2J0rHw@mail.gmail.com> <CA%2BhQ2%2Bim9nFfYnqDS2HgRbAzdf5D0iaLCmCYhfXQVVRMouUFuw@mail.gmail.com> <CAJnByzht-qfDcm8oEg1aSRyVBZ1ygPvc2eMuoyJcq4geueTZ0Q@mail.gmail.com> <CA%2BhQ2%2BiERgWJ=cdFB-cByfT3r11T1kKr-5HiuCYZY-rxbjf=XA@mail.gmail.com> <CAJnByziDzdR2C6DcSRNPtrWACLq0XFpe4X1Ek9yXtFP9ivqWQw@mail.gmail.com> <CA%2BhQ2%2BhjnuGo1xKgc8CQ7gP35tiaZG7%2BroZBmX8aBgb8qWnLgg@mail.gmail.com> <CAJnByzh-VrRZeYdpkRFtCUGEN_arFBkemcN7byb51XV6UPswyg@mail.gmail.com> <CA%2BhQ2%2BiMw3kxjpcZy77vgOEsfk2UY0-farh9C8RKXZHMU7D8kw@mail.gmail.com> <CAJnByzgsuNBhdfPJsGrrHcU79xjK%2Bdq2RENgUkbZcehFm8MUxg@mail.gmail.com> <CAJnByzgNZ9YsYd7tBgYxiQPvuS_VZbhZNGvsPS-0apCDga7XFA@mail.gmail.com> <CANpwN=uHk-VwOoFz7NaPE9A-0B=MAapqxJ-uyCBtn=oMdacYnw@mail.gmail.com> <CAJnByzgjEEAzmWZu7BsSWHXmpjUtZcqXFGN8umCqmvgME1Jv%2BA@mail.gmail.com> <CANpwN=tfqitQW0BTXA7bU%2BTfmP8=wr7gE8wAP=hjAamjD7ny9Q@mail.gmail.com> <CAJnByzi5WHHvwcrmEOkJOHf5SJekbTtQoUgLmPbMtwTotc8mzA@mail.gmail.com> <CAJnByzhJnrmiwiLEEQV0meg7%2BDnLJ6Jq_J=6L=35Z9Lgw1GcyA@mail.gmail.com> <CA%2BhQ2%2BjTXyYdN4N4aWOkDdkBr%2BD3quocHn%2Bc8MA%2Bxc9yLs9V4w@mail.gmail.com> <CAJnByzg0PCXCyjnypS_2%2BRhKB0mf_4s8X1niFiyfedaCLUku7Q@mail.gmail.com> <CAJnByzipicNHhmw0kGq0cXnfgXqq1xP0aJ4dqr12SryBV1Ny3w@mail.gmail.com> <CA%2B_eA9h3NL6Ga4=HRjEiDtNaANkR8m7oZ9%2BCCpoWVB%2BaYW3%2Btw@mail.gmail.com> <CAJnByziVfVJ6gX_aL%2BwFvmW9ZsfwPV1RRCkxgEbZMoe1kSo35A@mail.gmail.com>
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Hi, If you think it's a bug can you please open an issue on the github ( https://github.com/luigirizzo/netmap/issues)? 2017-11-24 22:11 GMT+01:00 Xiaoye Sun <Xiaoye.Sun@rice.edu>: > Hi Vincenzo, > > Let me clarify my problem. (please ignore the previous incompleted email) > > I have a program, which is an extension of bridge.c > https://github.com/luigirizzo/netmap/blob/master/apps/bridge/bridge.c > The only difference is that my program also generates customized packets > sent to the NIC directly. > These customized packets have increasing sequence numbers. > So, this program not only sends these customized packets but also forwards > packets between NIC and host stack using zerocopy. > The program only takes one NIC queue and there is only one thread. > > I think the problem is that there is a chance where netmap does not update > the pointer to the buffer even when NS_BUF_CHANGED is set (buf_idx is > changed). > Can you disable zerocopy in bridge.c to see if the problem goes away? This would be an useful information. > > Let's say the NIC tx ring has 4096 slots. The customized packet sequence > 16 is filled in the buffer of slot 2057. > The customized packets keep filling the slots until the next available > slot is 2056. > Do you mean that your program fills the TX ring slots 2057,2058...2054,2055 with custom packets? This would mean you filled all the available slots, since one slot is left empty. > Now the customised packet sequence 4111 is filled to 2056. > You cannot fill the slot 2056 if 2055 has not been NIOCTXYSINC'd. Aren't you using nm_ring_empty() and nm_ring_space() functions to check for available space in TX ring (assuming you update rinig->head/ring->cur before calling those functions)? Cheers, Vincenzo > Then the netmap program is notified that there is a packet from the host > stack sent to the NIC. > The netmap program swaps the buf_idx between slot 2057 and the > corresponding slot in the host rx ring and set the NS_BUF_CHANGED flag of > both slots. > Then the netmap program fills sequence 4112 to slot 2058. > However, the buffer swap seems not succeed so that the original content of > slot 2057 (sequence 16) is sent out. > So that at the receiver side, the receiver sees two sequence > 16s.(16,17...4110,4111,16,4112,4113). > > So think the root of the problem is that the buffer pointer is not always > successfully/timely updated even after the NS_BUF_CHANGED flag is set and > the buf_idx is updated. > > Best, > Xiaoye > > > > On Wed, Nov 22, 2017 at 7:39 AM, Vincenzo Maffione <v.maffione@gmail.com> > wrote: > >> Hi, >> >> 2017-11-21 7:51 GMT+01:00 Xiaoye Sun <Xiaoye.Sun@rice.edu>: >> >>> Hi, >>> >>> Recently I found another problem with netmap. I think this new problem >>> could be related to the problems in this threads so I just post the new >>> problem here. >>> >>> In my setup, I have a sender program having a netmap ring (a pair of >>> RX/TX ring) for the NIC and a ring for the host stack. The sender program >>> puts customized packets (each packet has a unique sequence number and the >>> sender sends the packet in a sequence number increasing order) to the NIC >>> TX ring directly and also forwards the packets from the host RX ring to >>> the >>> NIC TX ring using "zerocopy" by swapping the buffer indices. >>> However, the receiver sees duplicated customized packets. For example, in >>> the case where the ring size is 32 (32 slots in a ring) the order of the >>> sequence numbers the receiver see is 1,2,3,4,5,...,68,69,*70* >>> ,71,72,73,...,99,100,*70*,101,102,103,... . An interesting thing I >>> found is >>> that the "gaps" between these two duplicated packets (70 in the example) >>> are always a number very close to the ring size, 32 in this example. In >>> my >>> experiment, I use a ring with 4096 slots and the gap is always more than >>> 4090 and close to 4096. I verified that this duplication happens due to >>> the >>> sender, not the receiver. Assuming my sender's implementation is correct, >>> then this duplication may happen in netmap and the NIC driver (ixgbe). >>> >> >> Netmap itself doesn't do any duplication nor takes a look at the packets. >> It just passes >> down ring->cur/ring->head to the ixgbe driver (after validation). >> The ixgbe driver datapath is bypassed and replaced with a netmap-enabled >> datapath (see https://github.com/luigirizzo/ >> netmap/blob/master/LINUX/ixgbe_netmap_linux.h#L294-L461); >> no duplication should happen there as each netmap slot (1 TX packet) is >> used >> only once. >> >>> >>> >>> Thinking back to the original problem in this post, I think these >>> problems >>> may be related. It seems to me that there could be multiple threads >>> pulling >>> the packets from the NIC TX ring (or the thread moved to other CPUs when >>> the problem occurs) and these threads may run on different cores so that >>> the outdated content in the buffer may be sent out when new content is >>> written to the buffer. >>> >>> >> There are no such threads pulling from the NIC TX ring. Your application >> directly >> puts new packets to be transmitted in the netmap buffers referenced in >> the netmap TX >> ring. When then you call NIOCTXSYNC or poll(), all the new TX buffers >> (e.g. all >> the ones from the previous value ring->head (included) to the new value >> of ring->head (excluded)) >> are moved to the NIC TX ring. This happens in the context of your >> application thread, >> no worker threads are used. Then the NIC hardware starts the transmission. >> >> >>> I am wondering if there is a way to pin the NIC driver of the netmap >>> module >>> to a specific core. or is there a way to know the root of such problem? >>> >> >> The only threads are the ones of your application. >> Maybe your problem comes from concurrent accesses to the netmap TX ring >> from different threads? Only one thread at a given time should update a >> netmap >> TX/RX ring. Otherwise the behaviour is unspecified. >> >> Cheers, >> Vincenzo >> >> >>> >>> Best, >>> Xiaoye >>> >>> >> -- >> Vincenzo Maffione >> > > -- Vincenzo Maffione
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