grub2/0198-Make-pmtimer-tsc-calibration-not-take-51-seconds-to-.patch

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From 8df97294d653219ad03ac031c01b723ed7f6556d Mon Sep 17 00:00:00 2001
From: Peter Jones <pjones@redhat.com>
Date: Tue, 7 Nov 2017 17:12:17 -0500
Subject: [PATCH 198/198] Make pmtimer tsc calibration not take 51 seconds to
fail.
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 ~0x7998f9e TSCs, aka ~2
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.
Signed-off-by: Peter Jones <pjones@redhat.com>
---
grub-core/kern/i386/tsc_pmtimer.c | 43 ++++++++++++++++++++++++++++++---------
1 file changed, 33 insertions(+), 10 deletions(-)
diff --git a/grub-core/kern/i386/tsc_pmtimer.c b/grub-core/kern/i386/tsc_pmtimer.c
index c9c361699..609402b83 100644
--- a/grub-core/kern/i386/tsc_pmtimer.c
+++ b/grub-core/kern/i386/tsc_pmtimer.c
@@ -38,30 +38,53 @@ grub_pmtimer_wait_count_tsc (grub_port_t pmtimer,
grub_uint64_t start_tsc;
grub_uint64_t end_tsc;
int num_iter = 0;
+ int bad_reads = 0;
- start = grub_inl (pmtimer) & 0xffffff;
+ start = grub_inl (pmtimer) & 0x3fff;
last = start;
end = start + num_pm_ticks;
start_tsc = grub_get_tsc ();
while (1)
{
- cur = grub_inl (pmtimer) & 0xffffff;
+ cur = grub_inl (pmtimer);
+
+ /* 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 == 0xffffffff || cur == 0)
+ {
+ bad_reads++;
+ grub_dprintf ("pmtimer", "cur: 0x%08x bad_reads: %d\n", cur, bad_reads);
+
+ if (bad_reads == 10)
+ return 0;
+ }
+ else if (bad_reads)
+ bad_reads = 0;
+
+ cur &= 0x3fff;
+
if (cur < last)
- cur |= 0x1000000;
+ cur |= 0x4000;
num_iter++;
if (cur >= end)
{
end_tsc = grub_get_tsc ();
+ grub_dprintf ("pmtimer", "tsc delta is 0x%016lx\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. 5000 TSCs is between 5us (10GHz) and
+ 200us (250 MHz). If after this time we still don't have 1us on
+ pmtimer, then pmtimer is broken.
*/
- if ((num_iter & 0xffffff) == 0 && grub_get_tsc () - start_tsc > 5000000) {
- return 0;
- }
+ end_tsc = grub_get_tsc();
+ if ((num_iter & 0x3fff) == 0 && end_tsc - start_tsc > 5000)
+ {
+ grub_dprintf ("pmtimer", "tsc delta is 0x%016lx\n",
+ end_tsc - start_tsc);
+ return 0;
+ }
}
}
--
2.14.3