On Tue, 2007-06-05 at 12:01 +0200, Andi Kleen wrote:
> > But TSC is a "required feature", so "cpu_has_tsc" is always true.
>
> Hmm? It isn't. What makes you think so?
Interestingly it seems to be only in -mm.
> > How about this patch:
> > ===
> > Don't try to disable the TSC: it's a required feature under modern
> > configurations, so just mark the sched clock unstable which has the
> > same effect.
>
> No, using the cpuid bit is the correct way. Or better fix lguest to support
> TSC properly.
I have a patch for a tsc-based clock, but that's a little orthogonal: I
actually need to override sched_clock.
(I'd really like to do stolen time and everything, but looking at Xen
it's a lot of code to do right, and noone's asked for it yet).
This time for sure!
===
In recent -mm kernels, the TSC capability cannot be disabled,
resulting in a divide by zero error in the normal sched_clock.
The correct fix is to have a special lguest sched_clock
implementation: this is as simple as it gets.
Signed-off-by: Rusty Russell <[email protected]>
---
drivers/lguest/lguest.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
===================================================================
--- a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -351,11 +351,18 @@ static void lguest_time_irq(unsigned int
update_process_times(user_mode_vm(get_irq_regs()));
}
+static u64 sched_clock_base;
static void lguest_time_init(void)
{
set_irq_handler(0, lguest_time_irq);
hcall(LHCALL_TIMER_READ, 0, 0, 0);
+ sched_clock_base = jiffies_64;
enable_lguest_irq(0);
+}
+
+static unsigned long long lguest_sched_clock(void)
+{
+ return (jiffies_64 - sched_clock_base) * (1000000000 / HZ);
}
static void lguest_load_esp0(struct tss_struct *tss,
@@ -494,6 +501,7 @@ __init void lguest_init(void *boot)
paravirt_ops.time_init = lguest_time_init;
paravirt_ops.set_lazy_mode = lguest_lazy_mode;
paravirt_ops.wbinvd = lguest_wbinvd;
+ paravirt_ops.sched_clock = lguest_sched_clock;
hcall(LHCALL_LGUEST_INIT, __pa(&lguest_data), 0, 0);
@@ -507,8 +515,6 @@ __init void lguest_init(void *boot)
cpu_detect(&new_cpu_data);
/* Math is always hard! */
new_cpu_data.hard_math = 1;
-
- tsc_disable = 1;
#ifdef CONFIG_X86_MCE
mce_disabled = 1;
-
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