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[dm-devel] Re: [PATCH 07/18] io-controller: Export disk time used and nr sectors dipatched through cgroups



Vivek Goyal wrote:
> On Wed, May 13, 2009 at 10:39:07AM +0800, Gui Jianfeng wrote:
>> Vivek Goyal wrote:
>> ...
>>>  
>>> +/*
>>> + * traverse through all the io_groups associated with this cgroup and calculate
>>> + * the aggr disk time received by all the groups on respective disks.
>>> + */
>>> +static u64 calculate_aggr_disk_time(struct io_cgroup *iocg)
>>> +{
>>> +	struct io_group *iog;
>>> +	struct hlist_node *n;
>>> +	u64 disk_time = 0;
>>> +
>>> +	rcu_read_lock();
>>   This function is in slow-path, so no need to call rcu_read_lock(), just need to ensure
>>   that the caller already holds the iocg->lock.
>>
> 
> Or can we get rid of requirement of iocg_lock here and just read the io
> group data under rcu read lock? Actually I am wondering why do we require
> an iocg_lock here. We are not modifying the rcu protected list. We are
> just traversing through it and reading the data.

  Yes, i think removing the iocg->lock from caller(io_cgroup_disk_time_read()) 
  is a better choice.

> 
> Thanks
> Vivek
> 
>>> +	hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) {
>>> +		/*
>>> +		 * There might be groups which are not functional and
>>> +		 * waiting to be reclaimed upon cgoup deletion.
>>> +		 */
>>> +		if (rcu_dereference(iog->key))
>>> +			disk_time += iog->entity.total_service;
>>> +	}
>>> +	rcu_read_unlock();
>>> +
>>> +	return disk_time;
>>> +}
>>> +
>> -- 
>> Regards
>> Gui Jianfeng
> 
> 
> 

-- 
Regards
Gui Jianfeng


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