97 lines
3.0 KiB
Diff
97 lines
3.0 KiB
Diff
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From 8df97294d653219ad03ac031c01b723ed7f6556d Mon Sep 17 00:00:00 2001
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From: Peter Jones <pjones@redhat.com>
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Date: Tue, 7 Nov 2017 17:12:17 -0500
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Subject: [PATCH 198/198] Make pmtimer tsc calibration not take 51 seconds to
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fail.
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On my laptop running at 2.4GHz, if I run a VM where tsc calibration
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using pmtimer will fail presuming a broken pmtimer, it takes ~51 seconds
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to do so (as measured with the stopwatch on my phone), with a tsc delta
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of 0x1cd1c85300, or around 125 billion cycles.
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If instead of trying to wait for 5-200ms to show up on the pmtimer, we try
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to wait for 5-200us, it decides it's broken in ~0x7998f9e TSCs, aka ~2
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million cycles, or more or less instantly.
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Additionally, this reading the pmtimer was returning 0xffffffff anyway,
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and that's obviously an invalid return. I've added a check for that and
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0 so we don't bother waiting for the test if what we're seeing is dead
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pins with no response at all.
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Signed-off-by: Peter Jones <pjones@redhat.com>
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---
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grub-core/kern/i386/tsc_pmtimer.c | 43 ++++++++++++++++++++++++++++++---------
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1 file changed, 33 insertions(+), 10 deletions(-)
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diff --git a/grub-core/kern/i386/tsc_pmtimer.c b/grub-core/kern/i386/tsc_pmtimer.c
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index c9c361699..609402b83 100644
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--- a/grub-core/kern/i386/tsc_pmtimer.c
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+++ b/grub-core/kern/i386/tsc_pmtimer.c
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@@ -38,30 +38,53 @@ grub_pmtimer_wait_count_tsc (grub_port_t pmtimer,
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grub_uint64_t start_tsc;
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grub_uint64_t end_tsc;
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int num_iter = 0;
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+ int bad_reads = 0;
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- start = grub_inl (pmtimer) & 0xffffff;
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+ start = grub_inl (pmtimer) & 0x3fff;
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last = start;
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end = start + num_pm_ticks;
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start_tsc = grub_get_tsc ();
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while (1)
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{
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- cur = grub_inl (pmtimer) & 0xffffff;
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+ cur = grub_inl (pmtimer);
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+
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+ /* If we get 10 reads in a row that are obviously dead pins, there's no
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+ reason to do this thousands of times.
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+ */
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+ if (cur == 0xffffffff || cur == 0)
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+ {
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+ bad_reads++;
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+ grub_dprintf ("pmtimer", "cur: 0x%08x bad_reads: %d\n", cur, bad_reads);
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+
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+ if (bad_reads == 10)
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+ return 0;
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+ }
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+ else if (bad_reads)
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+ bad_reads = 0;
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+
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+ cur &= 0x3fff;
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+
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if (cur < last)
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- cur |= 0x1000000;
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+ cur |= 0x4000;
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num_iter++;
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if (cur >= end)
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{
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end_tsc = grub_get_tsc ();
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+ grub_dprintf ("pmtimer", "tsc delta is 0x%016lx\n",
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+ end_tsc - start_tsc);
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return end_tsc - start_tsc;
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}
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- /* Check for broken PM timer.
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- 50000000 TSCs is between 5 ms (10GHz) and 200 ms (250 MHz)
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- if after this time we still don't have 1 ms on pmtimer, then
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- pmtimer is broken.
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+ /* Check for broken PM timer. 5000 TSCs is between 5us (10GHz) and
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+ 200us (250 MHz). If after this time we still don't have 1us on
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+ pmtimer, then pmtimer is broken.
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*/
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- if ((num_iter & 0xffffff) == 0 && grub_get_tsc () - start_tsc > 5000000) {
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- return 0;
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- }
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+ end_tsc = grub_get_tsc();
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+ if ((num_iter & 0x3fff) == 0 && end_tsc - start_tsc > 5000)
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+ {
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+ grub_dprintf ("pmtimer", "tsc delta is 0x%016lx\n",
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+ end_tsc - start_tsc);
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+ return 0;
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+ }
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}
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}
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--
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2.14.3
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