Date: Wed, 25 Oct 2006 22:11:33 -0700 From: "Jack Vogel" <jfvogel@gmail.com> To: "Scott Long" <scottl@samsco.org> Cc: freebsd-net <freebsd-net@freebsd.org>, John Polstra <jdp@polstra.com> Subject: Re: em network issues Message-ID: <2a41acea0610252211w262e95c4k32e80d729475c0b9@mail.gmail.com> In-Reply-To: <454009DF.5000704@samsco.org> References: <XFMail.20061019152433.jdp@polstra.com> <200610251818.k9PIIe7p062530@ambrisko.com> <2a41acea0610251736n16cc4188h489f6d953130f91a@mail.gmail.com> <454009DF.5000704@samsco.org>
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On 10/25/06, Scott Long <scottl@samsco.org> wrote: > Jack Vogel wrote: > > On 10/25/06, Doug Ambrisko <ambrisko@ambrisko.com> wrote: > > > >> 3) In em_process_receive_interrupts/em_rxeof always decrement > >> the count on every run through the loop. If you notice > >> count is an is an int that starts at the passed in value > >> of -1. It then count-- until count==0. Doing -1, -2, -3 > >> takes awhile until the int rolls over to 0. Passing 100 > >> limits it more :-) So this can run 3 * 100 versuses > >> infinite * int roll over assuming we don't skip a count--. > > > > Been chatting with Jesse Brandeburg (one of our senior Linux guys) about > > receive side cleaning. Gave me a number of things to think about. First > > off, > > this change you mention is problematic. The reason it doesnt increment > > every time thru the while loop is its meant as a packet counter, NOT a > > descriptor counter. If we just fix this number at 100, and have it only > > counting descriptors you could get all but the EOP descriptor of a packet > > and then exit without finishing it and calling the stack, not a good > > tactic. > > > > Having a limited count is still a good idea, but I think we still want > > to base > > it on packets and not just descriptors. > > > > Jesse also talked about their experience with the Linux driver, deciding > > where to update the RDT, my current code doesnt do it til after the whole > > while loop is completed (havent looked at CURRENT again today yet), > > Jesse suggested doing it but not EVERY pass in the loop, maybe making > > it mod the number of rx descriptors. Having that AND a fixed limit on the > > number of total packets cleaned in a pass might be good. > > Good idea. Though for 1518 byte frames, I think you'll only have one > descriptor per packet. Definitely need to do the right thing for jumbo > frames, though. > > > > > I was also thinking, maybe having the taskqueue code be selectable, but > > not just a POLL vs TASKQUEUE, rather keep a legacy intr option which > > has a POLL option within it. > > > > My motivation for doing that is I can take the TASKQUEUE code into the > > Intel code base, but make it backward compatible, the default would have > > it optioned off. > > > > Jack > > I had it that way initially, and I think you commented that it was ugly > ;-) Naaahhhh, couldnt be, I'd never do anything like that :) OHHHH, I know what you're talking about. When I first started this job a year ago the driver was just PEPPERED with all these #if _FreeBSD_Version < BladdyFoo or something like that. I think the Intel code base was even worse cuz Tony was trying to make a single source base for 4.X and 5.X at that point. It was a major pain to look at that code :) What I'm talking about is a simple #ifdef EM_FASTINTR or something like that, no defines that remind me of POSIX header files please :) Jack
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