Date: Mon, 20 Nov 2017 16:11:44 -0800 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Xiaoye Sun <Xiaoye.Sun@rice.edu> Cc: Vincenzo Maffione <v.maffione@gmail.com>, FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: [netmap] when does a packet in the netmap ring send out exactly Message-ID: <CA%2BhQ2%2Bh0QEx3LPvFGNZv5ZvBJOJ-X0go-=c3V0gr6FRhe7icXA@mail.gmail.com> In-Reply-To: <CAJnByzhv27D_V=kyJjzQPQ28GM8kACKsH87MB5uDKVkQ-aka0g@mail.gmail.com> References: <CAJnByzh4Kzp6-DXXcB06QHSBJpHBKhtDnKUn7R%2BK0A_5VUThyw@mail.gmail.com> <CA%2B_eA9i5WOiA8j3y8fX65rzDLXEyt2B2wo8pK12jM2ZvEBURYg@mail.gmail.com> <CAJnByzhv27D_V=kyJjzQPQ28GM8kACKsH87MB5uDKVkQ-aka0g@mail.gmail.com>
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Hi, I think if you call the TXSYNC ioctl without advancing the head pointer, then the tail is advanced as much as possible. Cheers luigi On Mon, Nov 20, 2017 at 3:35 PM, Xiaoye Sun <Xiaoye.Sun@rice.edu> wrote: > Hi, > > I found that the tail pointer only moves when the ring has less than half > of the slots available. This prevents me from knowing the accurate time > when the packet in a slot is processed. Is there a way to move the tail > pointer as long as the packet in the slot is processed? Is this a > configurable feature? > > Best, > Xiaoye > > On Fri, Oct 27, 2017 at 11:52 AM, Vincenzo Maffione <v.maffione@gmail.com> > wrote: > >> Hi, >> This is actually a limitation of the netmap API: ring->tail is exposed >> to the user so that it knows it can use the slots in the range >> "[ring->head..ring->tail[" for new transmissions (note that head is >> included, tail excluded, to prevent wraparound). However, there is no >> explicit indication of "up to what slots packets were transmitted". >> For hw NICs, however, ring->tail is an indication of where transmission >> was completed. >> Example: >> 1) at the beginning ring->tail = ring->head = ring->cur = 0 >> 2) then your program moves head/cur forward: head = cur = 10 >> 3) you call TXSYNC, to submit the packets to the NIC. >> 4) after the TXSYNC call, is very likely that tail is still 0, i.e. >> because no transmission has been completed by the NIC (and no interrupt >> generated). >> 5) say after 20 us you issue another TXSYNC, and in the meanwhile 6 >> packets had completed. In this case after TXSYNC you will find tail==5, >> meaning that packets in the slots 0,1,2,3,4 and 5 have been completed. Note >> that also the slot pointed by tail has been completed. >> >> But you are right that there is no way to receive completion notification >> if the queue is not full. You must use TXSYNC to check (by sleeping or busy >> wait) when tail moves forward. >> >> Cheers, >> Vincenzo >> >> >> 2017-10-27 3:06 GMT+02:00 Xiaoye Sun <Xiaoye.Sun@rice.edu>: >> >>> Hi >>> >>> I write a netmap program that sends packets to the network. my program >>> uses one netmap ring and fills the ring slots with packets. >>> My program needs to do something (action A) after a particular packet >>> (packet P) in the ring slot is sent to the network. so the program tracks >>> the position of the tail point and checks if the tail point has moved >>> across the slot I used to put that packet P. >>> However, I found that the tail pointer may not move forward even seconds >>> after the receiver side got packet P. >>> Sometimes the tail pointer never moves forward until the TX ring is full. >>> I try ioctl(NIOCTXSYNC), however, it cannot 100% solve the problem. >>> >>> My question is that is there a way to make the TX ring empty as early as >>> possible so that I can know when my packet is sent out. or is there >>> another >>> way to know when the packet in the slot is sent to the network/NIC >>> physical >>> queue? >>> >>> I am using Linux 3.16.0-4-amd64. >>> >>> Thanks! >>> >>> Best, >>> Xiaoye >>> _______________________________________________ >>> freebsd-net@freebsd.org mailing list >>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >>> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >>> >> >> >> >> -- >> Vincenzo Maffione >> > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" -- -----------------------------------------+------------------------------- Prof. Luigi RIZZO, rizzo@iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/ . Universita` di Pisa TEL +39-050-2217533 . via Diotisalvi 2 Mobile +39-338-6809875 . 56122 PISA (Italy) -----------------------------------------+-------------------------------
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