Date: Thu, 17 Nov 2016 18:26:59 -0500 From: Paras Jha <dreadiscool@gmail.com> To: Vincenzo Maffione <v.maffione@gmail.com> Cc: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Advantages of Netmap NM_OPEN_NO_MMAP Message-ID: <CAMs8r4NUxH_2OR5xQ-fZyEFTvTzG9x=f7bzt=qjEc%2BZy9ei%2BSw@mail.gmail.com> In-Reply-To: <CA%2B_eA9gcsrcEHDvjctsRJMd0%2Bsf-McRPsGkeMNKAJ%2BZaxP5c2Q@mail.gmail.com> References: <CAMs8r4PZGUY=iOHm3P1XEZ7%2BcLEya%2B_hFCw-LGvL=50S47hwXQ@mail.gmail.com> <CA%2B_eA9gcsrcEHDvjctsRJMd0%2Bsf-McRPsGkeMNKAJ%2BZaxP5c2Q@mail.gmail.com>
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Hi, Thanks for the quick reply, it clarified things for me. Regarding the idea of independent TX-RX ring couples per thread, would a possible variation of this methodology be 1 RX ring per interface (only one thread reads), but *x* amount of TX rings, where *x *is the number of threads. Am I correct in assuming that such a structure will allow lockless zero-copy between an arbitrary number of interfaces (3 or greater)? Regards On Thu, Nov 17, 2016 at 5:11 PM, Vincenzo Maffione <v.maffione@gmail.com> wrote: > Hi, > No, each interface open in netmap mode has its own netmap buffers (for > packet data) and netmap rings, independently of what is the netmap memory > region where buffers/rings resides. > Two applications using different interfaces can work independently on each > other (no locks needed), it does not matter whether they are in the same > netmap memory region or not, because the data structures (rings and > buffers) are separated. > It does matter in terms of isolation, of course: two applications using > the same shared memory must trust each other. > > Typically you want two interfaces to be in the same netmap memory region > because you want an application to do zerocopy packet forwarding between > the two interfaces. > Also in this case locks are not usually needed, since you would have a > single thread accessing both interfaces. (Or you could have a separate > thread for each TX-RX ring couple, but always without using locks.) > > You can imagine a netmap memory region as a pool of buffers and rings, > where one or more interfaces can allocate their buffers/rings when they > enter netmap mode (deallocation is on exit from netmap mode). > Your system can have many memory regions. By default all the physical > interfaces share the same memory region, while each VALE port uses a > private memory region. > This is however being changed to ease arbitrary association between > interfaces and memory regions. > > Cheers, > Vincenzo > > 2016-11-17 22:50 GMT+01:00 Paras Jha <dreadiscool@gmail.com>: > >> Hi all, >> >> I had a quick question about some of the implications of sharing packet >> buffer memory between multiple interfaces. Assuming an arbitrary amount of >> interfaces (> 2) are linked together with NM_OPEN_NO_MMAP and share the >> same memory, would this have any issues with lock contention? >> >> Sorry in advance if this is the wrong place to post, I had seen several >> other archives about Netmap on this mailing list and I thought it was the >> most appropriate place. >> >> Regards >> _______________________________________________ >> 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 >
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