Messages in this thread | | | Date | Tue, 29 Nov 2016 12:31:08 -0500 | From | Tejun Heo <> | Subject | Re: [PATCH V4 15/15] blk-throttle: add latency target support |
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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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