Re: [PATCH 07/27] arm64: Substitute gettimeofday with C implementation

[Mark Salyzyn <salyzyn@android.com>]

On 11/09/2018 08:13 AM, Arnd Bergmann wrote:
>> diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
>> index beca249bc2f3..9de0ffc369c5 100644
>> --- a/arch/arm64/kernel/vdso/vdso.lds.S
>> +++ b/arch/arm64/kernel/vdso/vdso.lds.S
>> @@ -88,6 +88,7 @@ VERSION
>>                  __kernel_gettimeofday;
>>                  __kernel_clock_gettime;
>>                  __kernel_clock_getres;
>> +               __kernel_time;
>>          local: *;
>>          };
>>   }
> I would  prefer to not add any deprecated interfaces in the VDSO. If we
> have the 64-bit version of clock_gettime, we don't need the 32-bit version
> of it, and we don't need gettimeofday() or time() either. The C library
> can easily implement those by calling into clock_gettime.
Alas time() calls are simple and in the order of get_res, the cost of 
which is a five fold
improvement over the alternate higher resolution calls (clock_gettime or 
up to 100 fold
on some architectures over gettimeofday). We could measure a small 
improvement in
cpu utilization (and thus battery life by extension) attributed to arm64 
Android by
calling __kernel_time over __kernel_clock_gettime with coarse 
resolution. A game of
inches admittedly, but super KISS to add, and it is not as-if 
__kernel_time existence
will cause an issue with deprecation of a system call entry point.

-- Mark