Messages in this thread | | | Subject | Re: [PATCH v2 1/3] sched: Add helper kstat_cpu_softirqs_sum() | From | "Leizhen (ThunderTown)" <> | Date | Fri, 28 Oct 2022 10:38:15 +0800 |
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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
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