So what's wrong with something like:
struct cpu_idletime {
seqlock_t seqlock;
unsigned long nr_iowait;
u64 start;
u64 idle_time,
u64 iowait_time,
} __cacheline_aligned_in_smp;
DEFINE_PER_CPU(struct cpu_idletime, cpu_idletime);
void io_schedule(void)
{
struct cpu_idletime *it = __raw_get_cpu_var(cpu_idletime);
write_seqlock(&it->seqlock);
if (!it->nr_iowait++)
it->start = local_clock();
write_sequnlock(&it->seqlock);
current->in_iowait = 1;
schedule();
current->in_iowait = 0;
write_seqlock(&it->seqlock);
if (!--it->nr_iowait)
it->iowait_time += local_clock() - it->start;
write_sequnlock(&it->seqlock);
}
Afaict you don't need the preempt disable and atomic muck at all.
It will all get a little more complicated to deal with overlapping idle
and iowait times, but the idea is the same.
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