On Fri, Mar 13, 2020 at 08:06:33PM +0100, Javier Martinez Canillas wrote: > From: Peter Jones <pjo...@redhat.com> > > On my laptop running at 2.4GHz, if I run a VM where tsc calibration > using pmtimer will fail presuming a broken pmtimer, it takes ~51 seconds > to do so (as measured with the stopwatch on my phone), with a tsc delta > of 0x1cd1c85300, or around 125 billion cycles. > > If instead of trying to wait for 5-200ms to show up on the pmtimer, we try > to wait for 5-200us, it decides it's broken in ~0x2626aa0 TSCs, aka ~2.4 > million cycles, or more or less instantly. > > Additionally, this reading the pmtimer was returning 0xffffffff anyway, > and that's obviously an invalid return. I've added a check for that and > 0 so we don't bother waiting for the test if what we're seeing is dead > pins with no response at all. > > If "debug" is includes "pmtimer", you will see one of the following > three outcomes. If pmtimer gives all 0 or all 1 bits, you will see: > > pmtimer: 0xffffff bad_reads: 1 > pmtimer: 0xffffff bad_reads: 2 > pmtimer: 0xffffff bad_reads: 3 > pmtimer: 0xffffff bad_reads: 4 > pmtimer: 0xffffff bad_reads: 5 > pmtimer: 0xffffff bad_reads: 6 > pmtimer: 0xffffff bad_reads: 7 > pmtimer: 0xffffff bad_reads: 8 > pmtimer: 0xffffff bad_reads: 9 > pmtimer: 0xffffff bad_reads: 10 > timer is broken; giving up. > > This outcome was tested using qemu+kvm with UEFI (OVMF) firmware and > these options: -machine pc-q35-2.10 -cpu Broadwell-noTSX > > If pmtimer gives any other bit patterns but is not actually marching > forward fast enough to use for clock calibration, you will see: > > pmtimer delta is 0x0 (1904 iterations) > tsc delta is implausible: 0x2626aa0 > > This outcome was tested using grub compiled with GRUB_PMTIMER_IGNORE_BAD_READS > defined (so as not to trip the bad read test) using qemu+kvm with UEFI > (OVMF) firmware, and these options: -machine pc-q35-2.10 -cpu Broadwell-noTSX > > If pmtimer actually works, you'll see something like: > > pmtimer delta is 0xdff > tsc delta is 0x278756 > > This outcome was tested using qemu+kvm with UEFI (OVMF) firmware, and > these options: -machine pc-i440fx-2.4 -cpu Broadwell-noTSX > > I've also tested this outcome on a real Intel Xeon E3-1275v3 on an Intel > Server Board S1200V3RPS using the SDV.RP.B8 "Release" build here: > https://firmware.intel.com/sites/default/files/UEFIDevKit_S1200RP_vB8.zip > > Signed-off-by: Peter Jones <pjo...@redhat.com> > Signed-off-by: Javier Martinez Canillas <javi...@redhat.com>
It seems to me that this is very similar or even the same patch to https://lists.gnu.org/archive/html/grub-devel/2018-02/msg00067.html If yes I had some comments which were never resolved: https://lists.gnu.org/archive/html/grub-devel/2018-02/msg00078.html If you take my comments into account I am happy to get it into 2.06. Daniel > --- > > grub-core/kern/i386/tsc_pmtimer.c | 109 ++++++++++++++++++++++++------ > 1 file changed, 89 insertions(+), 20 deletions(-) > > diff --git a/grub-core/kern/i386/tsc_pmtimer.c > b/grub-core/kern/i386/tsc_pmtimer.c > index c9c36169978..412f5fe3c83 100644 > --- a/grub-core/kern/i386/tsc_pmtimer.c > +++ b/grub-core/kern/i386/tsc_pmtimer.c > @@ -28,40 +28,101 @@ > #include <grub/acpi.h> > #include <grub/cpu/io.h> > > +/* > + * Define GRUB_PMTIMER_IGNORE_BAD_READS if you're trying to test a timer > that's > + * present but doesn't keep time well. > + */ > +// #define GRUB_PMTIMER_IGNORE_BAD_READS > + > grub_uint64_t > grub_pmtimer_wait_count_tsc (grub_port_t pmtimer, > grub_uint16_t num_pm_ticks) > { > grub_uint32_t start; > - grub_uint32_t last; > - grub_uint32_t cur, end; > + grub_uint64_t cur, end; > grub_uint64_t start_tsc; > grub_uint64_t end_tsc; > - int num_iter = 0; > + unsigned int num_iter = 0; > +#ifndef GRUB_PMTIMER_IGNORE_BAD_READS > + int bad_reads = 0; > +#endif > > - start = grub_inl (pmtimer) & 0xffffff; > - last = start; > + /* > + * Some timers are 24-bit and some are 32-bit, but it doesn't make much > + * difference to us. Caring which one we have isn't really worth it since > + * the low-order digits will give us enough data to calibrate TSC. So just > + * mask the top-order byte off. > + */ > + cur = start = grub_inl (pmtimer) & 0x00ffffffUL; > end = start + num_pm_ticks; > start_tsc = grub_get_tsc (); > while (1) > { > - cur = grub_inl (pmtimer) & 0xffffff; > - if (cur < last) > - cur |= 0x1000000; > - num_iter++; > + cur &= 0xffffffffff000000ULL; > + cur |= grub_inl (pmtimer) & 0x00ffffffUL; > + > + end_tsc = grub_get_tsc(); > + > +#ifndef GRUB_PMTIMER_IGNORE_BAD_READS > + /* > + * If we get 10 reads in a row that are obviously dead pins, there's no > + * reason to do this thousands of times. > + */ > + if (cur == 0xffffffUL || cur == 0) > + { > + bad_reads++; > + grub_dprintf ("pmtimer", > + "pmtimer: 0x%"PRIxGRUB_UINT64_T" bad_reads: %d\n", > + cur, bad_reads); > + grub_dprintf ("pmtimer", "timer is broken; giving up.\n"); > + > + if (bad_reads == 10) > + return 0; > + } > +#endif > + > + if (cur < start) > + cur += 0x1000000; > + > if (cur >= end) > { > - end_tsc = grub_get_tsc (); > + grub_dprintf ("pmtimer", "pmtimer delta is 0x%"PRIxGRUB_UINT64_T"\n", > + cur - start); > + grub_dprintf ("pmtimer", "tsc delta is 0x%"PRIxGRUB_UINT64_T"\n", > + end_tsc - start_tsc); > return end_tsc - start_tsc; > } > - /* Check for broken PM timer. > - 50000000 TSCs is between 5 ms (10GHz) and 200 ms (250 MHz) > - if after this time we still don't have 1 ms on pmtimer, then > - pmtimer is broken. > + > + /* > + * Check for broken PM timer. 1ms at 10GHz should be 1E+7 TSCs; at > + * 250MHz it should be 2.5E5. So if after 4E+7 TSCs on a 10GHz > machine, > + * we should have seen pmtimer show 4ms of change (i.e. cur =~ > + * start+14320); on a 250MHz machine that should be 160ms > (start+572800). > + * If after this a time we still don't have 1ms on pmtimer, then > pmtimer > + * is broken. > + * > + * Likewise, if our code is perfectly efficient and introduces no > delays > + * whatsoever, on a 10GHz system we should see a TSC delta of 3580 in > + * ~3580 iterations. On a 250MHz machine that should be ~900 > iterations. > + * > + * With those factors in mind, there are two limits here. There's a > hard > + * limit here at 8x our desired pm timer delta, picked as an > arbitrarily > + * large value that's still not a lot of time to humans, because if we > + * get that far this is either an implausibly fast machine or the > pmtimer > + * is not running. And there's another limit on 4x our 10GHz tsc delta > + * without seeing cur converge on our target value. > */ > - if ((num_iter & 0xffffff) == 0 && grub_get_tsc () - start_tsc > > 5000000) { > - return 0; > - } > + if ((++num_iter > (grub_uint32_t)num_pm_ticks << 3UL) || > + end_tsc - start_tsc > 40000000) > + { > + grub_dprintf ("pmtimer", > + "pmtimer delta is 0x%"PRIxGRUB_UINT64_T" (%u > iterations)\n", > + cur - start, num_iter); > + grub_dprintf ("pmtimer", > + "tsc delta is implausible: 0x%"PRIxGRUB_UINT64_T"\n", > + end_tsc - start_tsc); > + return 0; > + } > } > } > > @@ -74,12 +135,20 @@ grub_tsc_calibrate_from_pmtimer (void) > > fadt = grub_acpi_find_fadt (); > if (!fadt) > - return 0; > + { > + grub_dprintf ("pmtimer", "No FADT found; not using pmtimer.\n"); > + return 0; > + } > pmtimer = fadt->pmtimer; > if (!pmtimer) > - return 0; > + { > + grub_dprintf ("pmtimer", "FADT does not specify pmtimer; skipping.\n"); > + return 0; > + } > > - /* It's 3.579545 MHz clock. Wait 1 ms. */ > + /* > + * It's 3.579545 MHz clock. Wait 1 ms. > + */ > tsc_diff = grub_pmtimer_wait_count_tsc (pmtimer, 3580); > if (tsc_diff == 0) > return 0; > -- > 2.24.1 _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel