On 06/28/2017 03:54 PM, Jens Axboe wrote:
> On 06/28/2017 03:12 PM, Brian King wrote:
>> -static inline int part_in_flight(struct hd_struct *part)
>> +static inline unsigned long part_in_flight(struct hd_struct *part)
>> {
>> - return atomic_read(&part->in_flight[0]) + atomic_read(&part->in_flight[1]);
>> + return part_stat_read(part, in_flight[0]) + part_stat_read(part, in_flight[1]);
>
> One obvious improvement would be to not do this twice, but only have to
> loop once. Instead of making this an array, make it a structure with a
> read and write count.
>
> It still doesn't really fix the issue of someone running on a kernel
> with a ton of possible CPUs configured. But it does reduce the overhead
> by 50%.
Or something as simple as this:
#define part_stat_read_double(part, field1, field2) \
({ \
typeof((part)->dkstats->field1) res = 0; \
unsigned int _cpu; \
for_each_possible_cpu(_cpu) { \
res += per_cpu_ptr((part)->dkstats, _cpu)->field1; \
res += per_cpu_ptr((part)->dkstats, _cpu)->field2; \
} \
res; \
})
static inline unsigned long part_in_flight(struct hd_struct *part)
{
return part_stat_read_double(part, in_flight[0], in_flight[1]);
}
--
Jens Axboe
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