On 9/29/21 10:24 AM, Hao Xu wrote: > 在 2021/9/28 下午6:51, Pavel Begunkov 写道: >> On 9/26/21 11:00 AM, Hao Xu wrote: [...] >>> I'm gonna pick this one up again, currently this patch >>> with ktime_get_ns() works good on our productions. This >>> patch makes the latency a bit higher than before, but >>> still lower than aio. >>> I haven't gotten a faster alternate for ktime_get_ns(), >>> any hints? >> >> Good, I'd suggest to look through Documentation/core-api/timekeeping.rst >> In particular coarse variants may be of interest. >> https://www.kernel.org/doc/html/latest/core-api/timekeeping.html#coarse-and-fast-ns-access >> > The coarse functions seems to be like jiffies, because they use the last > timer tick(from the explanation in that doc, it seems the timer tick is > in the same frequency as jiffies update). So I believe it is just > another format of jiffies which is low accurate. I haven't looked into the details, but it seems that unlike jiffies for the coarse mode 10ms (or whatever) is the worst case, but it _may_ be much better on average and feasible for your case, but can't predict if that's really the case in a real system and what will be the relative error comparing to normal ktime_ns(). -- Pavel Begunkov
