Re: [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in function pvclock_read_flags

[Paolo Bonzini]

On 07/06/2016 15:16, Minfei Huang wrote:
> ping. Any comment is appreciate.

The patch looks good, I'll follow up with another to introduce the
seqcount-like read_begin/read_retry API.

Thanks,

Paolo

> On 05/28/16 at 08:27P, Minfei Huang wrote:
>> There is a generic function __pvclock_read_cycles to be used to get both
>> flags and cycles. For function pvclock_read_flags, it's useless to get
>> cycles value. To make this function be more effective, get this variable
>> flags directly in function.
>>
>> Signed-off-by: Minfei Huang <mnghuan@xxxxxxxxx>
>> ---
>> v1:
>> - Get rid of __pvclock_read_cycles according to Andy's suggestion
>> ---
>>  arch/x86/kernel/pvclock.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
>> index 7f82fe0..06c58ce 100644
>> --- a/arch/x86/kernel/pvclock.c
>> +++ b/arch/x86/kernel/pvclock.c
>> @@ -61,11 +61,14 @@ void pvclock_resume(void)
>>  u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
>>  {
>>  	unsigned version;
>> -	cycle_t ret;
>>  	u8 flags;
>>  
>>  	do {
>> -		version = __pvclock_read_cycles(src, &ret, &flags);
>> +		version = src->version;
>> +		/* Make the latest version visible */
>> +		smp_rmb();
>> +
>> +		flags = src->flags;
>>  		/* Make sure that the version double-check is last. */
>>  		smp_rmb();
>>  	} while ((src->version & 1) || version != src->version);
>> -- 
>> 2.6.3
>>
>