On Wed, Mar 23, 2016 at 09:58:42AM +0200, Konstantin Belousov wrote: > If TSC has the behaviour you described, i.e. suddenly jumping random > steps on single CPU, from the point of view of kernel, then the system > is seriosly misbehaving. The timekeeping stuff would be badly broken > regardless of the ipi_wait(). I do not see why should we worry about > that in ipi_wait(). > > I proposed slightly different thing, i.e. using timekeep code to indirect > to TSC if configured so. Below is the proof of concept patch, use of > nanouptime() may be too naive, and binuptime() would cause tiny bit less > overhead, but I do not want to think about arithmetic. > > diff --git a/sys/x86/x86/local_apic.c b/sys/x86/x86/local_apic.c > index 7e5087b..fdc12a4 100644 > --- a/sys/x86/x86/local_apic.c > +++ b/sys/x86/x86/local_apic.c > @@ -1621,31 +1621,37 @@ SYSINIT(apic_setup_io, SI_SUB_INTR, SI_ORDER_THIRD, > apic_setup_io, NULL); > * private to the MD code. The public interface for the rest of the > * kernel is defined in mp_machdep.c. > */ > + > +/* > + * Wait delay microseconds for IPI to be sent. If delay is -1, we > + * wait forever. > + */ > static int > native_lapic_ipi_wait(int delay) > { > - int x; > + struct timespec end, x; > > /* LAPIC_ICR.APIC_DELSTAT_MASK is undefined in x2APIC mode */ > if (x2apic_mode) > return (1); > > - /* > - * Wait delay microseconds for IPI to be sent. If delay is > - * -1, we wait forever. > - */ > - if (delay == -1) { > - while ((lapic_read_icr_lo() & APIC_DELSTAT_MASK) != > - APIC_DELSTAT_IDLE) > - ia32_pause(); > - return (1); > + if (delay != -1) { > + KASSERT(delay > 0, ("wrong delay %d", delay)); > + x.tv_sec = delay / 1000000; > + x.tv_nsec = (delay % 1000000) * 1000; > + nanouptime(&end); > + timespecadd(&end, &x); > } > - > - for (x = 0; x < delay; x++) { > + for (;;) { > if ((lapic_read_icr_lo() & APIC_DELSTAT_MASK) == > APIC_DELSTAT_IDLE) > return (1); > - DELAY(1); > + ia32_pause(); > + if (delay != -1) { > + nanouptime(&x); > + if (timespeccmp(&x, &end, >)) > + break; > + } > } > return (0); > }
Of course this cannot work if timecounter takes any locks, even spinlock. Only TSC or similar lock-less mechanisms are allowed there. Meh. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"