Date: Mon, 24 Sep 2007 11:47:48 -0400 From: John Baldwin <jhb@freebsd.org> To: "Attilio Rao" <attilio@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/amd64/amd64 local_apic.c src/sys/i386/acpica madt.c src/sys/i386/i386 local_apic.c src/sys/kern subr_smp.c src/sys/sun4v/mdesc mdesc_init.c Message-ID: <200709241147.49288.jhb@freebsd.org> In-Reply-To: <3bbf2fe10709211338j6dbab59am1ad67c86c1a05baa@mail.gmail.com> References: <200709112254.l8BMsB7P074637@repoman.freebsd.org> <200709211436.15444.jhb@freebsd.org> <3bbf2fe10709211338j6dbab59am1ad67c86c1a05baa@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Friday 21 September 2007 04:38:47 pm Attilio Rao wrote: > 2007/9/21, John Baldwin <jhb@freebsd.org>: > > On Tuesday 11 September 2007 06:54:09 pm Attilio Rao wrote: > > > attilio 2007-09-11 22:54:09 UTC > > > > > > FreeBSD src repository > > > > > > Modified files: > > > sys/amd64/amd64 local_apic.c > > > sys/i386/acpica madt.c > > > sys/i386/i386 local_apic.c > > > sys/kern subr_smp.c > > > sys/sun4v/mdesc mdesc_init.c > > > Log: > > > This is a follow-up, cleaning-up commit about recent changes involving > > > topology foo functions. > > > Working at the patch for topology problems in ia32/amd64 evicted some > > > problems regarding functions ordering in the SI_SUB_CPU family of > > > SYSINIT'ed subsystems. > > > In order to avoid problems with new modified to involved functions, a > > > correct ordering is not semantically specified for SI_SUB_CPU functions > > > (for a larger view of the issue please visit: > > > http://lists.freebsd.org/pipermail/freebsd-current/2007-July/075409.html ) > > > > Could you clarify exactly what ordering this does? AFAICT, nothing in > > cpu_startup() requires the APIC to be up and running. If there were a > > dependency, then that would be something for the MD architecture code to fix. > > IIUC, the problem was that you had 3 sysinit functions like this: > > > > A - SI_ORDER_FIRST, cpu_startup() > > B - SI_ORDER_FIRST, apic_init() > > C - SI_ORDER_SECOND, mp_start() > > > > Now mp_start() requires both A and B to have run on x86. What Peter did > > originally was to move B to SI_ORDER_SECOND because he found that B needed A > > to run. That broke because C could end up running before B. However, the > > actual patch that went into CVS left A and B as is and instead made them > > independent of each other so B no longer depends on A. So, I don't think > > you've solved an actual problem. > > I know exactly what was the problem as I diagnosed the problem when B > was in SI_ORDER_FIRST and I diagnosed the problem when B was moved > temporally in SI_ORDER_SECOND while C was taking this slot. > > Basically what about people adding code in A which introduces > dependency with B? It results in a problem > This ordering doesn't break anything and it makes the code safe for > further changes. It's a gratuitous change if you aren't actually _fixing_ anything. I think there is a fundamental thing you are missing here though: it is ok to have multiple SYSINIT's with the same subsystem and order if they are independent. All device drivers register themselves with new-bus at the same subsystem and order for example. There is no need to "dream up" a false ordering if it is not needed. Now you have made B always come after A. What if a future code change makes A depend on B? It is best to solve these problems when they appear. > > The madt.c change in this commit is plain wrong however and should be > > reverted. If it was correct it would have needed to be done in amd64's > > madt.c as well. > > Plain wrong? > You mean maybe that it doesn't matter that (SI_ORDER_CPU -1) was > shared with mptable_register()? And what about if someone adds > dependency between the two? madt changes are perfectly working as they > don't explicitly require to run before of mptable_register(). > And to be precise, there is no madt_register() in amd64, so I have no > idea what are you speaking about. :(. I guess you don't understand what these register routines do. The APIC code basically is a driver framework and APIC drivers (well, I call them APIC enumerators) register themselves with the core APIC code. These drivers/enumerators are then probed and the highest priority wins. Having these register routines at the same SYSINIT is identical to having all new-bus drivers register themselves with new-bus at the same level. They will never have any dependency on each other. % grep madt_register amd64/acpica/madt.c static void madt_register(void *dummy); madt_register(void *dummy __unused) SYSINIT(madt_register, SI_SUB_TUNABLES - 1, SI_ORDER_FIRST, madt_register, NULL) AMD64 looks for CPUs at at different time, so it uses SI_SUB_TUNABLES rather than SI_SUB_CPU, but it still has both mptable_register() and madt_register() at the same level/order and for a good reason. > > The sun4v change is bogus as well as mdesc_init() doesn't depend on > > cpu_startup() on sun4v at all, and it doesn't matter what order they run in. > > Reading this I think I see there is basically a misunderstanding of > what I wanted to do: I don't want to fix an actual problem but the > idea is to give to any function in SI_SUB_CPU a precise order in order > to avoid mistakes as the last ones people get trying to fix topology. > I think this is a legitimate idea. > And in particular, I don't like the approach 'just do things when you > need them'. See above. Are you going to go throw and assign a static order to ever device driver now just in case the one's registration routine might someday depend on another? > > Basically, I think at the least you should revert all the MD changes, and the > > change to subr_smp.c is basically a NOP. > > I'm not going to do this as the patch gives a precise ordering to all > functions involved in SI_SUB_CPU, doesn't break anything. > If you don't like the ordering due please just explain why. It hardcodes an ordering that isn't there and that might have to be reworked in the future if a real dependency does show up that is not the order you currently just randomly chose. -- John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200709241147.49288.jhb>