Date: Sun, 26 Nov 2017 22:06:56 -0800 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r326218 - head/sys/kern Message-ID: <abfdf2b1-bb2f-4eb1-a448-bfee68158577@freebsd.org> In-Reply-To: <3170692.kvv90QqB0X@ralph.baldwin.cx> References: <201711252341.vAPNf5Qx001464@repo.freebsd.org> <3170692.kvv90QqB0X@ralph.baldwin.cx>
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On 11/26/17 20:50, John Baldwin wrote: > On Saturday, November 25, 2017 11:41:05 PM Nathan Whitehorn wrote: >> Author: nwhitehorn >> Date: Sat Nov 25 23:41:05 2017 >> New Revision: 326218 >> URL: https://svnweb.freebsd.org/changeset/base/326218 >> >> Log: >> Remove some, but not all, assumptions that the BSP is CPU 0 and that CPUs >> are numbered densely from there to n_cpus. >> >> MFC after: 1 month >> >> Modified: >> head/sys/kern/kern_clock.c >> head/sys/kern/kern_clocksource.c >> head/sys/kern/kern_shutdown.c >> head/sys/kern/kern_timeout.c >> head/sys/kern/sched_ule.c >> head/sys/kern/subr_pcpu.c >> >> Modified: head/sys/kern/kern_clock.c >> ============================================================================== >> --- head/sys/kern/kern_clock.c Sat Nov 25 23:23:24 2017 (r326217) >> +++ head/sys/kern/kern_clock.c Sat Nov 25 23:41:05 2017 (r326218) >> @@ -573,7 +573,9 @@ hardclock_cnt(int cnt, int usermode) >> void >> hardclock_sync(int cpu) >> { >> - int *t = DPCPU_ID_PTR(cpu, pcputicks); >> + int *t; >> + KASSERT(!CPU_ABSENT(cpu), ("Absent CPU %d", cpu)); > Blank line before the KASSERT() perhaps? > >> + t = DPCPU_ID_PTR(cpu, pcputicks); >> >> *t = ticks; > Probably don't need this blank line though? Those are both good ideas. > >> } >> >> Modified: head/sys/kern/sched_ule.c >> ============================================================================== >> --- head/sys/kern/sched_ule.c Sat Nov 25 23:23:24 2017 (r326217) >> +++ head/sys/kern/sched_ule.c Sat Nov 25 23:41:05 2017 (r326218) >> @@ -2444,6 +2451,7 @@ sched_add(struct thread *td, int flags) >> * Pick the destination cpu and if it isn't ours transfer to the >> * target cpu. >> */ >> + td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid to start */ >> cpu = sched_pickcpu(td, flags); > It is not obvious why every sched_add() needs this once you've fixed thread0. > Shouldn't new threads just inherit from thread0's already-fixed value? If not, > perhaps fix thread0's value sooner? That's a fair point. I don't remember the rationale for this now; the changes are over a year old from the powernv branch. I do remember setting thread0's CPU early not working, but have forgotten why. I will try to remember... >> tdq = sched_setcpu(td, cpu, flags); >> tdq_add(tdq, td, flags); >> >> Modified: head/sys/kern/subr_pcpu.c >> ============================================================================== >> --- head/sys/kern/subr_pcpu.c Sat Nov 25 23:23:24 2017 (r326217) >> +++ head/sys/kern/subr_pcpu.c Sat Nov 25 23:41:05 2017 (r326218) >> @@ -279,6 +279,8 @@ pcpu_destroy(struct pcpu *pcpu) >> struct pcpu * >> pcpu_find(u_int cpuid) >> { >> + KASSERT(cpuid_to_pcpu[cpuid] != NULL, >> + ("Getting uninitialized PCPU %d", cpuid)); > This KASSERT seems unnecessary? If the caller uses an invalid one, it will > just fault anyway. It won't necessarily fault. For example, on PowerPC, NULL is a valid address that does not trigger faults. It's unfortunately quite complicated to fix this in a general way. Even if it did fault, this makes the fault more informative (and has found at least one bug on arm64 already). > >> return (cpuid_to_pcpu[cpuid]); >> } >> @@ -409,7 +411,7 @@ DB_SHOW_ALL_COMMAND(pcpu, db_show_cpu_all) >> int id; >> >> db_printf("Current CPU: %d\n\n", PCPU_GET(cpuid)); >> - for (id = 0; id <= mp_maxid; id++) { >> + CPU_FOREACH(id) { > If you remove the KASSERT you don't need this change since it checks the return > value of pcpu_find() (which you didn't change). In particular, this DDB command > shows all valid pcpu structures safely even if that set is inconsistent with > the all_cpus mask (or the old version did at least). There is also nothing about > this that assumes BSP == 0 either. CPU_FOREACH() is doing a loop from 0 to > mp_maxid under the covers as well. True. CPU_FOREACH just seemed simpler here and future-proof if it ever started doing something more complex. -Nathan > >> pc = pcpu_find(id); >> if (pc != NULL) { >> show_pcpu(pc); >> >
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