Il 20/03/2014 10:57, James Hogan ha scritto:
> On 19/03/14 16:29, Paolo Bonzini wrote:
>> Il 14/03/2014 13:47, James Hogan ha scritto:
>>> From: Sanjay Lal <sanjayl@xxxxxxxxxxx>
>>>
>>> Compare/Count timer interrupts are handled in-kernel for KVM, so don't
>>> bother starting it in QEMU.
>>>
>>> Signed-off-by: Sanjay Lal <sanjayl@xxxxxxxxxxx>
>>> Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
>>> Reviewed-by: Aurelien Jarno <aurelien@xxxxxxxxxxx>
>>> ---
>>> Changes in v2:
>>> - Expand commit message
>>> - Rebase on v1.7.0
>>> - Wrap comment
>>> ---
>>> hw/mips/cputimer.c | 13 ++++++++++---
>>> 1 file changed, 10 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/mips/cputimer.c b/hw/mips/cputimer.c
>>> index c8b4b00..52570fd 100644
>>> --- a/hw/mips/cputimer.c
>>> +++ b/hw/mips/cputimer.c
>>> @@ -23,6 +23,7 @@
>>> #include "hw/hw.h"
>>> #include "hw/mips/cpudevs.h"
>>> #include "qemu/timer.h"
>>> +#include "sysemu/kvm.h"
>>>
>>> #define TIMER_FREQ 100 * 1000 * 1000
>>>
>>> @@ -141,7 +142,13 @@ static void mips_timer_cb (void *opaque)
>>>
>>> void cpu_mips_clock_init (CPUMIPSState *env)
>>> {
>>> - env->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, &mips_timer_cb, env);
>>> - env->CP0_Compare = 0;
>>> - cpu_mips_store_count(env, 1);
>>> + /*
>>> + * If we're in KVM mode, don't start the periodic timer, that is
>>> handled in
>>> + * kernel.
>>> + */
>>> + if (!kvm_enabled()) {
>>> + env->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, &mips_timer_cb,
>>> env);
>>> + env->CP0_Compare = 0;
>>> + cpu_mips_store_count(env, 1);
>>> + }
>>> }
>>>
>>
>> I hate to make you do unrelated changes, but... initializing CP0_Compare
>> is unnecessary, it should already be 0;
>
> You mean because of the memset in object_initialize_with_type, when
> object_new is called? Although that wouldn't handle reset, although
> technically the reset state of Compare is undefined.
No, see mips_cpu_reset:
static void mips_cpu_reset(CPUState *s)
{
MIPSCPU *cpu = MIPS_CPU(s);
MIPSCPUClass *mcc = MIPS_CPU_GET_CLASS(cpu);
CPUMIPSState *env = &cpu->env;
mcc->parent_reset(s);
memset(env, 0, offsetof(CPUMIPSState, mvp));
tlb_flush(s, 1);
cpu_state_reset(env);
}
Fields before mvp are reset to zero (including CP0_Compare and CP0_Count).
> Am I right that the correct way to prevent clock drift is for
> kvm_arch_put_registers to only set the Count register if level !=
> KVM_PUT_RUNTIME_STATE?
Yes, that makes sense. Or, better, do not provide a set_onereg
interface for CP0_Count. Instead, in the kernel you can base the CPU
timer on the value of CLOCK_MONOTONIC, like this:
+static inline u64 get_monotonic_ns(void)
+{
+ struct timespec ts;
+
+ ktime_get_ts(&ts);
+ return timespec_to_ns(&ts);
+}
+
Then you provide three set_onereg interfaces. One is normal cp0_count,
but it is only used if the timer is not running (according to
cp0_cause). The second is the rate at which the timer counts
(cp0_count_hz). The third is used when the timer is running, and
it is:
cp0_count_bias
= cp0_count * 10^9 / cp0_count_hz - get_monotonic_ns()
So when the timer is running cp0_count is computed as follows:
cp0_count =
= (get_monotonic_ns() + cp0_count_bias) * cp0_count_hz / 10^9
QEMU can then set:
cp0_count = cpu_mips_get_count(env)
cp0_count_bias =
cpu_mips_get_count(env) * 10^9 / cp0_count_hz - qemu_get_clock_ns(rt_clock)
Note that QEMU's qemu_get_clock_ns(rt_clock) == kernel's get_monotonic_ns().
So when the guest reads cp0_count (and the timer was running at the time
kvm_arch_put_registers was set), the kernel will return:
cp0_count =
= (get_monotonic_ns() + cp0_count_bias) * cp0_count_hz / 10^9
= env->cp0_count
+ (get_monotonic_ns() - qemu_get_clock_ns(rt_clock)
+ qemu_get_clock_ns(vm_clock)) * cp0_count_hz / 10^9
= env->cp0_count + qemu_get_clock_ns(vm_clock) * cp0_count_hz / 10^9
= cpu_mips_get_count(env)
Paolo
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