Hello,
On Mon, Nov 14, 2016 at 02:22:22PM -0800, Shaohua Li wrote:
> One hard problem adding .high limit is to detect idle cgroup. If one
> cgroup doesn't dispatch enough IO against its high limit, we must have a
> mechanism to determine if other cgroups dispatch more IO. We added the
> think time detection mechanism before, but it doesn't work for all
> workloads. Here we add a latency based approach.
As I wrote before, I think that the two mechanisms should operate on
two mostly separate aspects of io control - latency control for
arbitrating active cgroups and idle detection to count out cgroups
which are sitting doing nothing - instead of the two meachanisms
possibly competing.
> static bool throtl_tg_is_idle(struct throtl_grp *tg)
> {
> - /* cgroup is idle if average think time is more than threshold */
> - return ktime_get_ns() - tg->last_finish_time >
> + /*
> + * cgroup is idle if:
> + * 1. average think time is higher than threshold
> + * 2. average request size is small and average latency is higher
^
lower, right?
> + * than target
> + */
So, this looks like too much magic to me. How would one configure for
a workload which may issue small IOs, say, every few seconds but
requries low latency?
Thanks.
--
tejun
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