Re: [PATCH v1 01/14] xen/riscv: implement get_s_time()

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

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On 4/10/25 2:52 PM, Jan Beulich wrote:
> On 08.04.2025 17:57, Oleksii Kurochko wrote:
>> @@ -23,6 +24,11 @@ static inline cycles_t get_cycles(void)
>>       return csr_read(CSR_TIME);
>>   }
>>   
>> +static inline s_time_t ticks_to_ns(uint64_t ticks)
>> +{
>> +    return muldiv64(ticks, SECONDS(1), 1000 * cpu_khz);
>> +}
> Why the extra multiplication by 1000? I.e. why not
> "muldiv64(ticks, MILLISECONDS(1), cpu_khz)", getting away with just one
> multiplication and a reduced risk of encountering intermediate overflow
> (affecting only hypothetical above 4THz CPUs then)?

Multiplication by 1000 was needed to convert khz to hz, but yes, your option
would be better.

>
>> --- a/xen/arch/riscv/time.c
>> +++ b/xen/arch/riscv/time.c
>> @@ -4,10 +4,17 @@
>>   #include <xen/init.h>
>>   #include <xen/lib.h>
>>   #include <xen/sections.h>
>> +#include <xen/types.h>
>>   
>>   unsigned long __ro_after_init cpu_khz; /* CPU clock frequency in kHz. */
>>   uint64_t __ro_after_init boot_clock_cycles;
>>   
>> +s_time_t get_s_time(void)
>> +{
>> +    uint64_t ticks = get_cycles() - boot_clock_cycles;
>> +    return ticks_to_ns(ticks);
> Nit: Blank line between declaration(s) and statement(s) please, as well as
> ahead of the main "return" of a function.
>
> Happy to make both adjustments upon committing, so long as you agree; then:
> Reviewed-by: Jan Beulich<jbeulich@suse.com>

I'll be happy with that.

Thank you very much.

~ Oleksii

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