Date: Mon, 7 Dec 2009 23:28:40 -0500 From: Alexander Sack <pisymbol@gmail.com> To: Scott Long <scottl@samsco.org> Cc: scottl@freebsd.org, freebsd-current@freebsd.org, emaste@freebsd.org, Jung-uk Kim <jkim@freebsd.org> Subject: Re: aac(4) resource FIB starvation on BUS scan revisited Message-ID: <3c0b01820912072028g4146523fxf9c649913095365e@mail.gmail.com> In-Reply-To: <3c0b01820912072017x7d85c9e3t875692d7264bc05@mail.gmail.com> References: <3c0b01820912071342u1c722b2clf9c8413e40097279@mail.gmail.com> <200912071931.46002.jkim@FreeBSD.org> <D7DDDA30-44B2-4E84-9F52-42DD2C43DC62@samsco.org> <200912072005.02662.jkim@FreeBSD.org> <3A549504-2AFE-4133-A8EF-642D53BC9F73@samsco.org> <3c0b01820912072000l7ad1a67ek3514dfccb96417be@mail.gmail.com> <0FFC216C-E938-48E4-B0E4-351077C6088A@samsco.org> <3c0b01820912072017x7d85c9e3t875692d7264bc05@mail.gmail.com>
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On Mon, Dec 7, 2009 at 11:17 PM, Alexander Sack <pisymbol@gmail.com> wrote: > On Mon, Dec 7, 2009 at 11:04 PM, Scott Long <scottl@samsco.org> wrote: >> >> On Dec 7, 2009, at 9:00 PM, Alexander Sack wrote: >> >>> On Mon, Dec 7, 2009 at 8:14 PM, Scott Long <scottl@samsco.org> wrote: >>>> >>>> On Dec 7, 2009, at 6:05 PM, Jung-uk Kim wrote: >>>>> >>>>> On Monday 07 December 2009 07:47 pm, Scott Long wrote: >>>>>> >>>>>> On Dec 7, 2009, at 5:31 PM, Jung-uk Kim wrote: >>>>>>> >>>>>>> On Monday 07 December 2009 05:30 pm, Alexander Sack wrote: >>>>>>>> >>>>>>>> On Mon, Dec 7, 2009 at 4:42 PM, Alexander Sack >>>>>>>> <pisymbol@gmail.com> >>>>>>> >>>>>>> wrote: >>>>>>>>> >>>>>>>>> Folks: >>>>>>>>> >>>>>>>>> I posted a similar thread on freebsd-scsi only to realize that >>>>>>>>> scottl had fixed my first issue during some MP CAM cleanup with >>>>>>>>> respect to a race during resource allocation issues on a later >>>>>>>>> version of the driver we are using (I believe we did the same >>>>>>>>> thing to resolve a lock issue on bootup). >>>>>>>>> >>>>>>>>> However on my RELENG_8 box with (2) Adaptec 5085s connected to >>>>>>>>> some JBODs (9TB each) I still have a FIB starvation issue >>>>>>>>> during the LUN scan: >>>>>>>>> >>>>>>>>> The number of FIBs allocated to this card is 512 (older cards >>>>>>>>> are 256). The max_target per bus is 287. On a six channel >>>>>>>>> controller with a BUS scan done in parallel I see a lot of >>>>>>>>> this: >>>>>>>>> >>>>>>>>> ... >>>>>>>>> (probe501:aacp1:0:214:0): Request Requeued >>>>>>>>> (probe501:aacp1:0:214:0): Retrying Command >>>>>>>>> (probe520:aacp1:0:233:0): Request Requeued >>>>>>>>> (probe520:aacp1:0:233:0): Retrying Command >>>>>>>>> (probe528:aacp1:0:241:0): Request Requeued >>>>>>>>> (probe528:aacp1:0:241:0): Retrying Command >>>>>>>>> (probe540:aacp1:0:253:0): Request Requeued >>>>>>>>> (probe540:aacp1:0:253:0): Retrying Command >>>>>>>>> (probe541:aacp1:0:254:0): Request Requeued >>>>>>>>> (probe541:aacp1:0:254:0): Retrying Command >>>>>>>>> .... >>>>>>>>> >>>>>>>>> I think the driver is much happier with the following attached >>>>>>>>> patch (with dmesg). >>>>>>>> >>>>>>>> Patch again but this time not base-64 encoded: >>>>>>> >>>>>>> [SNIP!] >>>>>>> >>>>>>> I want it to be little conservative here, i.e., pre-allocating >>>>>>> half of max_fibs. Will the attached patch work for you? >>>>>> >>>>>> The FIB allocation scheme was written when it was common for >>>>>> machines to only have 64MB of RAM and proportionally less KVA, so >>>>>> 256KB or 512KB was a lot of RAM to wire down. Those days have >>>>>> probably passed. >>>>> >>>>> So, what would do if you were hypothetically rewriting it today? :-) >>>>> >>>> >>>> Most hardware have mechanisms for probing their command queue depth. >>>> What I >>>> typically do these days is allocate a minimum number of commands so that >>>> this probing can be done, then do a single slab allocation based on the >>>> results. AAC doesn't have this capability, but the 256/512 size is >>>> pretty >>>> well understood. The page-by-page allocation of aac works, but adds >>>> extra >>>> bookkeeping and complication to the driver. >>>> >>> >>> Right Scott, that is what JK and I discussed this evening. I figured >>> the 128 macro was just historical cruft and your email confirms it. >>> So are we ALL okay with the original patch as it stands for now? JK I >>> am fine with the divide 2 change but I think raising it to 256 is >>> really the way to go at this point! :D >> >> >> If you're going to increase it, why not simply increase it to the max amount >> that is appropriate for each card? > > Totally right! I thought though that the max fibs variable was set my > reading firmware bits up. Am I off? > > 1755 /* Check for broken hardware that does a lower number of > commands */ > 1756 sc->aac_max_fibs = (sc->flags & AAC_FLAGS_256FIBS ? 256:512); > 1757 > > So checking against sc->aac_max_fibs would yield 512 up front on > modern controllers. > >> One other thing I forgot to mention was contiguous memory. The page-by-page >> allocation in aac has another benefit, and that's to not tax contigmalloc >> with finding 256KB of contiguous memory. That's not a big deal at boot, but >> is a problem if you load the driver after the system has been running for a >> while. It's immensely useful during development, but it's never been clear >> to me how useful it is in real life. > > True. I can't imagine even today after loading it, it would be THAT > much of an issue (besides its a RAID controller, do you really think > you are going to load it so late in the game?). > > I am filing PR as we speak just to track! http://www.freebsd.org/cgi/query-pr.cgi?pr=141269 I botched the category though, it should probably be "scsi" please... -aps
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