Date: Tue, 11 Dec 2012 09:56:16 -0500 From: Karim Fodil-Lemelin <fodillemlinkarim@gmail.com> To: freebsd-net@freebsd.org Cc: nodens2099@gmail.com Subject: Re: igb and ALTQ in 9.1-rc3 Message-ID: <50C74990.2090803@gmail.com> In-Reply-To: <CAPBZQG030sSLT__b4cYA2e07t-77pvv9S3f8HnZfYpsXKEqTkQ@mail.gmail.com> References: <20121211075853.GU48639@FreeBSD.org> <1355231140.51621.YahooMailClassic@web121603.mail.ne1.yahoo.com> <CAPBZQG030sSLT__b4cYA2e07t-77pvv9S3f8HnZfYpsXKEqTkQ@mail.gmail.com>
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On 11/12/2012 9:15 AM, Ermal Luçi wrote: > On Tue, Dec 11, 2012 at 2:05 PM, Barney Cordoba <barney_cordoba@yahoo.com>wrote: > >> >> --- On Tue, 12/11/12, Gleb Smirnoff <glebius@FreeBSD.org> wrote: >> >>> From: Gleb Smirnoff <glebius@FreeBSD.org> >>> Subject: Re: igb and ALTQ in 9.1-rc3 >>> To: "Jack Vogel" <jfvogel@gmail.com> >>> Cc: "Clement Hermann (nodens)" <nodens2099@gmail.com>, "Barney Cordoba" >> <barney_cordoba@yahoo.com>, freebsd-net@FreeBSD.org >>> Date: Tuesday, December 11, 2012, 2:58 AM >>> On Mon, Dec 10, 2012 at 03:31:19PM >>> -0800, Jack Vogel wrote: >>> J> UH, maybe asking the owner of the driver would help >>> :) >>> J> >>> J> ... and no, I've never been aware of doing anything to >>> stop supporting altq >>> J> so you wouldn't see any commits. If there's something >>> in the altq code or >>> J> support (which I have nothing to do with) that caused >>> this no-one informed >>> J> me. >>> >>> Switching from if_start to if_transmit effectively disables >>> ALTQ support. >>> >>> AFAIR, there is some magic implemented in other drivers that >>> makes them >>> modern (that means using if_transmit), but still capable to >>> switch to queueing >>> mode if SIOCADDALTQ was casted upon them. >>> >> It seems pretty difficult to say that something is compatible with >> something else if it hasn't been tested in a few years. >> >> It seems to me that ATLQ is the one that should handle if_transmit. >> although it's a good argument for having a raw "send" function in >> drivers. Ethernet drivers don't need more than a send() routing that >> loads a packet into the ring. The decision on what to do if you can't >> queue a packet should be in the network layer, if we must still call >> things layers. >> >> "start" is a leftover from a day when you stuffed a buffer and waited >> for an interrupt to stuff in another. The whole idea is antiquated. >> >> Imagine drivers that pull packets off of a card and simply queue it; >> and that you simply submit a packet to be queued for transmit. Instead >> of trying to find 35 programmers that understand all of the lock BS, >> you only need to have a couple. >> >> I always disable all of the gobbledegook like checksum offloading. They >> just muddy the water and have very little effect on performance. A modern >> cpu can do a checksum as fast as you can manage the "capabilities" without >> disrupting the processing path. >> >> With FreeBSD, every driver is an experience. Some suck so bad that they >> should come with a warning. The MSK driver is completely useless, as >> an example. >> >> >> BC >> _______________________________________________ >> freebsd-net@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-net >> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >> > During implementation of if_transmit altq was not considered at all. > The default if_transmit provides some compatibility but that is void since > altq has not been converted to call if_transmit after processing the mbuf. > > ALTQ can be adapted quite easily to if_transmit model it just wasn't done > at the time. > With if_transmit model it can even be modularized and not be a compile > kernel option since the queue of the iface is abstracted now. > > I have always wanted to do a diff but have not yet got to it. > The change is quite simple just provide an altq_transmit default method and > just hook into if_transmit model on the fly. > You surely need to handle some iface events and enable altq based on > request but its is not a hard to implement. > > I will always have this in my TODO but not sure when i can get to it. > The issue is not only that igb doesn't support if_transmit or if_start method but that ALTQ isn't multiqueue ready and still uses the IFQ_LOCK for all of its enqueue/dequeue operations. A simple drop in of if_transmit is bound to cause race conditions on any multiqueue driver with ALTQ. I do have a patch set for this on igb but its ugly and needs more work although it should get you going. Let me know if your interested I will clean it up and send it over. For more information on ALTQ discussion and igb please read this thread: http://freebsd.1045724.n5.nabble.com/em-igb-if-transmit-drbr-and-ALTQ-td5760338.html Best regards, Karim.
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