On Mon, Sep 16 2024 at 12:12, Thomas Gleixner wrote:
> On Sat, Sep 14 2024 at 13:07, Jeff Layton wrote:
>> + do {
>> + seq = read_seqcount_begin(&tk_core.seq);
>> +
>> + ts->tv_sec = tk->xtime_sec;
>> + mono = tk->tkr_mono.base;
>> + nsecs = timekeeping_get_ns(&tk->tkr_mono);
>> + offset = *offsets[TK_OFFS_REAL];
>> + } while (read_seqcount_retry(&tk_core.seq, seq));
>> +
>> + mono = ktime_add_ns(mono, nsecs);
>> +
>> + if (atomic64_try_cmpxchg(&mg_floor, &old, mono)) {
>> + ts->tv_nsec = 0;
>> + timespec64_add_ns(ts, nsecs);
>> + } else {
>> + /*
>> + * Something has changed mg_floor since "old" was
>> + * fetched. "old" has now been updated with the
>> + * current value of mg_floor, so use that to return
>> + * the current coarse floor value.
>
> 'Something has changed' is a truly understandable technical
> explanation.
old = mg_floor
mono = T1;
mg_floor = mono
preemption
do {
mono = T2;
}
cmpxchg fails and the function returns a value based on T1
No?
Thanks,
tglx
