Date: Wed, 28 Dec 2011 12:15:23 +0100 From: Stefan Bethke <stb@lassitu.de> To: Adrian Chadd <adrian@freebsd.org> Cc: "freebsd-embedded@freebsd.org" <freebsd-embedded@freebsd.org> Subject: Re: Updated switch/glue patch? Message-ID: <12538AED-175C-4B1E-BF05-6FD05D14CE70@lassitu.de> In-Reply-To: <CAJ-VmomZeHEyue4eaNGm%2Bw67uDBsOH_2bqocXjBGxyxHXStZ_A@mail.gmail.com> References: <CAJ-Vmon8%2BOXQ4g752zZEB-O0BR0sFWO0QUvw--xp2jsBDkx6tQ@mail.gmail.com> <0F6CC18F-6973-42A2-AC03-F01BF59458AE@lassitu.de> <CAJ-Vmo=Y8pp4iFnw%2B1hcPae6QXFboz=a7puwgC1kVSZ3JwMgPQ@mail.gmail.com> <1100F70E-9DA9-4163-AC9A-423ECE5AA9A3@lassitu.de> <CAJ-VmonrnJ7cC6u2LsL9AGusz_%2BkSwY62Rr1__sg5U_NynJ1SQ@mail.gmail.com> <CAJ-Vmo=WSN1oLM=B2HqSHrWyOaOD9BSwwu8=1Wys0CLRJ_N-TA@mail.gmail.com> <C637C171-A1A2-4296-84FA-6DE97137DC42@lassitu.de> <CAJ-Vmon2boy7OCh_4O0MeCi0yCdZu0OYb5dxHCEK=-%2B46zBGtg@mail.gmail.com> <CAJ-Vmoku5eLEYi5_DXVxK=0=4Ewn2aGepv3YUw4ApuVh_7y2%2Bw@mail.gmail.com> <CAJ-VmonvpnaS1rAO%2BsDRh1E5WfsrZTYE297Kc96prhfKjrM89Q@mail.gmail.com> <CAJ-VmokQxQs2DUKL=ONyxnnS7Q28ytmwZJ_thqvc4SvMkmS=cQ@mail.gmail.com> <18CABB46-9B9A-41CB-8742-6723C5FF4D67@lassitu.de> <C0BF20FD-E30F-4E9C-A0FE-500BE4807B99@bsdimp.com> <CAJ-VmokgiQCEG4et3X=3o_MuCMkO9MqkKqa-fjdpEqQNucn=Lw@mail.gmail.com> <2CBD8651-E132-49DC-A082-37A8F5C626EA@bsdimp.com> <AFE755D6-E462-40B4-A97B-9261303B3A4F@lassitu.de> <CAJ-Vm okwSHN8U2=HJQT9kxFQ9oE-6H2h3KDb%2BMHN1Z8sur9=yw@mail.gmail.com> <45529EC2-73BE-4F69-A9BE-E22D9FEAADD7@lassitu.de> <CAJ-VmonmMASxJZBAd2doX4eV6s5TF-3kCB0pLSMrWM8r0UsCmg@mail.gmail.com> <FC8A0B08-5292-44CC-AEC0-08BF170FCEA4@lassitu.de> <267FB3D6-830E-4A2F-8C1C-A96873EDCD31@lassitu.de> <EC4D4397-FA60-4CB1-8635-48988215E19A@lassitu.de> <CAJ-VmomZeHEyue4eaNGm%2Bw67uDBsOH_2bqocXjBGxyxHXStZ_A@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Am 28.12.2011 um 07:54 schrieb Adrian Chadd: > Hi, >=20 > I have a few questions: >=20 > * are you testing this all out with the -HEAD debugging enabled? ie, > witness, invariants, etc? Yes, just for my last test I disabled witness to run the test with max. = speed. > * Why'd you rename the mutex in the rtl8366rb driver from sc->sc_mtx > to sc->smi_mtx ? That's a spurious change; in an interim version, I had two mutexes (one = for the callout, one for the bus access). > * Why are you creating the callout w/out the lock now, rather than > with a lock? non-locked callouts make it more difficult to cancel > cleanly/atomically. With the mutex, I had trouble. I can't recall right now what exactly it = was. > * Are this smi_*_lockheld() functions designed to be called with > sc_smi_mtx held? If so, add a lock assertion macro there. Will do. > * You call DELAY() with the lock held: >=20 > + DELAY(RTL_IICBUS_PHYDELAY); /* chip > needs time to talk to PHY */ >=20 > .. why not use pause() instead? I don't like how it could result in > that particular mutex being held for far, far too long (and I'm > starting to be weary of mutexes being used as a way of serialising > slow device access, but I digress).. I'll give it a shot. > * You've implemented retries here, which make sense. How then does the > Linux driver work? Or is it doing retries and I just don't remember. The linux driver, as far as I can tell, never actually talks to the = PHYs, unless you compile it with debugging. > * The older iicbb code with the original timeout doesn't result in any > timeouts at all, just FYI. I'm happy with the idea of a faster, more > efficient iicbb where the driver also handles timeouts correctly.. I > just wonder whether we're making it more complicated. I'm fairly confident that the HEAD iicbb.c is slow and partially broken = (the waitack function in particular). I believe the reason you're = seeing no timeouts with that code is due to it being slow, plus not = reporting errors properly. > How is it OpenWRT/Linux doesn't end up suffering from these high CPU > spikes when doing bitbanged GPIO? Or are they seeing them but > preemption is just masking it? They do not talk to the PHYs. BTW, with the newest iteration of rtl8366rb.c, the callout reads three = registers, instead of five PHYs times three registers, which turns into = 5*3*3=3D30 rtl8366rb register accesses. In my testing, I couln't "feel" the slowdown anymore, even with WITNESS = enabled. Stefan --=20 Stefan Bethke <stb@lassitu.de> Fon +49 151 14070811
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?12538AED-175C-4B1E-BF05-6FD05D14CE70>