Messages in this thread | | | Date | Thu, 05 Nov 2015 11:29:29 -0500 | From | Waiman Long <> | Subject | Re: [PATCH tip/locking/core v9 4/6] locking/pvqspinlock: Collect slowpath lock statistics |
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On 11/02/2015 11:40 AM, Peter Zijlstra wrote: > On Fri, Oct 30, 2015 at 07:26:35PM -0400, Waiman Long wrote: >> This patch enables the accumulation of kicking and waiting related >> PV qspinlock statistics when the new QUEUED_LOCK_STAT configuration >> option is selected. It also enables the collection of data which >> enable us to calculate the kicking and wakeup latencies which have >> a heavy dependency on the CPUs being used. >> >> The statistical counters are per-cpu variables to minimize the >> performance overhead in their updates. These counters are exported >> via the sysfs filesystem under the /sys/kernel/qlockstat directory. >> When the corresponding sysfs files are read, summation and computing >> of the required data are then performed. > Why did you switch to sysfs? You can create custom debugfs files too.
I was not aware of that capability. So you mean using debugfs_create_file() using custom file_operations. Right? That doesn't seem to be easier than using sysfs. However, I can use that if you think it is better to use debugfs.
> >> @@ -259,7 +275,7 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node) >> if (READ_ONCE(pn->state) == vcpu_hashed) >> lp = (struct qspinlock **)1; >> >> - for (;;) { >> + for (;; waitcnt++) { >> for (loop = SPIN_THRESHOLD; loop; loop--) { >> if (!READ_ONCE(l->locked)) >> return; > Did you check that goes away when !STAT ?
Yes, the increment code goes away when !STAT. I had added a comment to talk about that.
> >> +/* >> + * Return the average kick latency (ns) = pv_latency_kick/pv_kick_unlock >> + */ >> +static ssize_t >> +kick_latency_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) >> +{ >> + int cpu; >> + u64 latencies = 0, kicks = 0; >> + >> + for_each_online_cpu(cpu) { > I think you need for_each_possible_cpu(), otherwise the results will > change with hotplug operations.
Right, I will make the change.
Cheers, Longman
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