diff mbox

KVM: i8254: Clean up limit constant

Message ID 4FD5C89D.2010408@siemens.com
State New
Headers show

Commit Message

Jan Kiszka June 11, 2012, 10:29 a.m. UTC 
On 2012-06-11 12:07, Avi Kivity wrote:
> On 06/06/2012 05:28 PM, Jan Kiszka wrote:
>> Due to a offset between the clock used to generate the in-kernel
>> count_load_time (CLOCK_MONOTONIC) and the clock used for processing this
>> in userspace (vm_clock), reading back the output of PIT channel 2 via
>> port 0x61 was broken. One use cases that suffered from it was the CPU
>> frequency calibration of SeaBIOS, which also affected IDE/AHCI timeouts.
>>
>> This fixes it by calibrating the offset between both clocks on
>> kvm_pit_get and adjusting the kernel value before saving it in the
>> userspace state. As the calibration only works while the vm_clock is
>> running, we cache the in-kernel state across stopped phases.
> 
> Applied, thanks.
> 
>> +    clock_offset = LLONG_MAX;
> 
> INT64_MAX would me more strictly correct, but in practice it makes no
> difference.

Was looking for this, just not long enough. Need to print some cheat
sheet. However, let's clean this up immediately:

---8<---

clock_offset is int64_t.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 hw/kvm/i8254.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

Comments

Avi Kivity June 11, 2012, 11:18 a.m. UTC | #1 
On 06/11/2012 01:29 PM, Jan Kiszka wrote:
> On 2012-06-11 12:07, Avi Kivity wrote:
>> On 06/06/2012 05:28 PM, Jan Kiszka wrote:
>>> Due to a offset between the clock used to generate the in-kernel
>>> count_load_time (CLOCK_MONOTONIC) and the clock used for processing this
>>> in userspace (vm_clock), reading back the output of PIT channel 2 via
>>> port 0x61 was broken. One use cases that suffered from it was the CPU
>>> frequency calibration of SeaBIOS, which also affected IDE/AHCI timeouts.
>>>
>>> This fixes it by calibrating the offset between both clocks on
>>> kvm_pit_get and adjusting the kernel value before saving it in the
>>> userspace state. As the calibration only works while the vm_clock is
>>> running, we cache the in-kernel state across stopped phases.
>> 
>> Applied, thanks.
>> 
>>> +    clock_offset = LLONG_MAX;
>> 
>> INT64_MAX would me more strictly correct, but in practice it makes no
>> difference.
> 
> Was looking for this, just not long enough. Need to print some cheat
> sheet. However, let's clean this up immediately:
> 
> ---8<---
> 
> clock_offset is int64_t.
> 

Thanks, folded.
diff mbox

Patch

diff --git a/hw/kvm/i8254.c b/hw/kvm/i8254.c
index 04333d8..c5d3711 100644
--- a/hw/kvm/i8254.c
+++ b/hw/kvm/i8254.c
@@ -62,7 +62,7 @@  static void kvm_pit_get(PITCommonState *pit)
      * kvm_pit_channel_state::count_load_time, and vm_clock. Take the
      * minimum of several samples to filter out scheduling noise.
      */
-    clock_offset = LLONG_MAX;
+    clock_offset = INT64_MAX;
     for (i = 0; i < CALIBRATION_ROUNDS; i++) {
         offset = qemu_get_clock_ns(vm_clock);
         clock_gettime(CLOCK_MONOTONIC, &ts);