On 08/13/2017 03:44 PM, Tejun Heo wrote: > Hello, Waiman. > > On Fri, Aug 11, 2017 at 04:19:07PM -0400, Waiman Long wrote: >>> * CPU usage stats are collected and shown in "cgroup.stat" with "cpu." >>> prefix. Total usage is collected from scheduling events. User/sys >>> breakdown is sourced from tick sampling and adjusted to the usage >>> using cputime_adjuts(). >> Typo: cputime_adjust() > Oops, will fix. > >>> +static DEFINE_MUTEX(cgroup_stat_mutex); >>> +static DEFINE_PER_CPU(raw_spinlock_t, cgroup_cpu_stat_lock); >> If the hierarchy is large enough and the stat data hasn't been read >> recently, it may take a while to accumulate all the stat data even for >> one cpu in cgroup_stat_flush_locked(). So I think it will make more >> sense to use regular spinlock_t instead of raw_spinlock_t. > They need to be raw spinlocks because the accounting side may grab > them while scheduling. If the accumulating latency becomes > problematic, we can test for need_resched and spin_needbreak and break > out as necessary. The iteration logic is built to allow that and an > earlier revision actually did that but I wasn't sure whether it's > actually necessary and removed it for simplicity. > > If the latency ever becomes a problem, resurrecting that isn't > difficult at all. Right, I forgot they will be used by the scheduler. I think it is prudent to limit the latency, but it can be another patch when the need arises. >>> +static struct cgroup *cgroup_cpu_stat_next_updated(struct cgroup *pos, >>> + struct cgroup *root, int cpu) >> This function is trying to unwind one cgrp from the updated_children and >> updated_next linkage. It is somewhat like the opposite of >> cgroup_cpu_stat_updated(). I just feel like its name isn't intuitive >> enough to convey what it is doing. Maybe use name like >> cgroup_cpu_stat_unlink_one() to match cgroup_cpu_stat_flush_one(). > Hmm... the name comes from it being an iterator - most interators are > named _next. But, yeah, the name doesn't signifiy that it unlinks as > it goes along. I'll rename it to cgroup_cpu_stat_pop_updated(). I am fine with that. Thanks, Longman -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
