On 2022/10/28 3:04, Elliott, Robert (Servers) wrote:
>
>> Similar to kstat_cpu_irqs_sum(), it counts the sum of all software
>> interrupts on a specified CPU.
>>
>> diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
>> @@ -67,6 +67,17 @@ static inline unsigned int kstat_softirqs_cpu(unsigned int irq, int cpu)
>> return kstat_cpu(cpu).softirqs[irq];
>> }
>>
>> +static inline unsigned int kstat_cpu_softirqs_sum(int cpu)
>> +{
>> + int i;
>> + unsigned int sum = 0;
>> +
>> + for (i = 0; i < NR_SOFTIRQS; i++)
>> + sum += kstat_softirqs_cpu(i, cpu);
>> +
>> + return sum;
>> +}
>
> In the function upon which this is based:
>
> struct kernel_stat {
> unsigned long irqs_sum;
> unsigned int softirqs[NR_SOFTIRQS];
> };
>
> static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu)
> {
> return kstat_cpu(cpu).irqs_sum;
> }
>
> kstat_cpu_irqs_sum returns an unsigned long as an unsigned int, which
> could cause large values to be truncated. Should that return
> unsigned long? The only existing caller is fs/proc/stat.c which
This should be a mistake on:
commit f2c66cd8eeddedb4 ("/proc/stat: scalability of irq num per cpu")
I'll correct it to "unsigned long" in the next version. Thanks.
> puts it into a u64:
> u64 sum = 0;
> ...
> sum += kstat_cpu_irqs_sum(i);
>
> The softirqs field is an unsigned int, so the new function doesn't have
> this inconsistency.
OK.
To be honest, I did the math. CONFIG_HZ=250
2^32 / 250 / 3600 / 24 / 365 = 0.545 < 1 year
So, in theory, for those 32-bit processors, we should use "unsigned long long".
Of course, from a programming point of view, 64-bit consists of two 32-bits,
and there is an atomicity problem. I think that's probably why members of
struct kernel_stat don't use u64.
However, it seems that the type of member softirqs can currently be changed to
unsigned long. So, at least on a 64-bit processor, it won't have a count
overflow problem.
>
> .
>
--
Regards,
Zhen Lei
