Date: Fri, 21 Sep 2007 22:38:47 +0200 From: "Attilio Rao" <attilio@freebsd.org> To: "John Baldwin" <jhb@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: <3bbf2fe10709211338j6dbab59am1ad67c86c1a05baa@mail.gmail.com> In-Reply-To: <200709211436.15444.jhb@freebsd.org> References: <200709112254.l8BMsB7P074637@repoman.freebsd.org> <200709211436.15444.jhb@freebsd.org>
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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. > 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. :(. > 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'. > 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. Attilio -- Peace can only be achieved by understanding - A. Einstein
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