I'm somewhat nervous about *requiring* that the per-CPU page be pinned in the TLB. Sure, that's how it works today, but if it ever changed, it would lead to subtle sporadic failures in sched_clock(). Also, I believe that with your patch applied, sched_clock() would fail (return 0) if a data-debug breakpoint was set on the area that it's reading and debug-faults are deferred.
--david On 8/16/05, Jason Uhlenkott <[EMAIL PROTECTED]> wrote: > Turning on PRINTK_TIME causes us to die in early boot when sched_clock() > tries to access per-cpu data which isn't set up yet. > > We can avoid this by doing a speculative load on the per-cpu data and > just returning zero if we fail. This matches the way sched_clock() > appears to behave on most other arches if it gets called before we > know the cpu frequency. > > Signed-off-by: Jason Uhlenkott <[EMAIL PROTECTED]> > > Index: linux/arch/ia64/kernel/head.S > =================================================================== > --- linux.orig/arch/ia64/kernel/head.S 2005-08-15 15:54:56.130313231 -0700 > +++ linux/arch/ia64/kernel/head.S 2005-08-16 12:49:23.843747550 -0700 > @@ -983,9 +983,10 @@ > addl r8=THIS_CPU(cpu_info) + IA64_CPUINFO_NSEC_PER_CYC_OFFSET,r0 > mov.m r9=ar.itc // fetch cycle-counter > (35 cyc) > ;; > - ldf8 f8=[r8] > + ldf8.s f8=[r8] > ;; > setf.sig f9=r9 // certain to stall, so issue it _after_ > ldf8... > + chk.s r8, .recover > ;; > xmpy.lu f10=f9,f8 // calculate low 64 bits of 128-bit product > (4 cyc) > xmpy.hu f11=f9,f8 // calculate high 64 bits of 128-bit product > @@ -995,6 +996,10 @@ > ;; > shrp r8=r9,r8,IA64_NSEC_PER_CYC_SHIFT > br.ret.sptk.many rp > +.recover: // per-cpu data isn't set up yet, > + // so just return 0. > + mov r8=r0 > + br.ret.sptk.many rp > END(sched_clock) > > GLOBAL_ENTRY(start_kernel_thread) > - > To unsubscribe from this list: send the line "unsubscribe linux-ia64" in > the body of a message to [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Mosberger Consulting LLC, voice/fax: 510-744-9372, http://www.mosberger-consulting.com/ 35706 Runckel Lane, Fremont, CA 94536 - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
