Re: [PATCH 3/6 v4] cfq-iosched: Introduce vdisktime and io weightfor CFQ queue

[Gui Jianfeng]

Vivek Goyal wrote:
> On Thu, Feb 10, 2011 at 03:47:16PM +0800, Gui Jianfeng wrote:
> 
> [..]
>> +/*
>> + * The time when a CFQ queue is put onto a service tree is recoreded in
>> + * cfqq->reposition_time. Currently, we check the first priority CFQ queues
>> + * on each service tree, and select the workload type that contains the lowest
>> + * reposition_time CFQ queue among them.
>> + */
>>  static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
>>  				struct cfq_group *cfqg, enum wl_prio_t prio)
>>  {
>>  	struct cfq_entity *cfqe;
>> +	struct cfq_queue *cfqq;
>> +	unsigned long lowest_start_time;
>>  	int i;
>> -	bool key_valid = false;
>> -	unsigned long lowest_key = 0;
>> +	bool time_valid = false;
>>  	enum wl_type_t cur_best = SYNC_NOIDLE_WORKLOAD;
>>  
>> +	/*
>> +	 * TODO: We may take io priority and io class into account when
>> +	 * choosing a workload type. But for the time being just make use of
>> +	 * reposition_time only.
>> +	 */
>>  	for (i = 0; i <= SYNC_WORKLOAD; ++i) {
>> -		/* select the one with lowest rb_key */
>>  		cfqe = cfq_rb_first(service_tree_for(cfqg, prio, i));
>> -		if (cfqe &&
>> -		    (!key_valid || time_before(cfqe->rb_key, lowest_key))) {
>> -			lowest_key = cfqe->rb_key;
>> +		cfqq = cfqq_of_entity(cfqe);
>> +		if (cfqe && (!time_valid ||
>> +			     time_before(cfqq->reposition_time,
>> +					 lowest_start_time))) {
>> +			lowest_start_time = cfqq->reposition_time;
> 
> Gui,
> 
> Have you had a chance to run some mixed workloads in a group (some sync,
> some async and some sync-idle queues), and see how latency and throughput
> of sync-idle workload changes due to this "resposition_time" logic. I 
> just want to make sure that latency of sync-noidle workload does not
> go up as that's the workload that people care and gets noticed first.

Hi Vivek,

I made a quick test by using fio. It seems the number changes little
between vanilla kernel and patched kernel.


Vanilla:    SYNC read            SYNC-NOIDLE read      ASYNC write  
         1. 23,640KB/s 5.40 ---- 6,696KB/s 19.07 ---- 50,142KB/s 128.00
         2. 24,459KB/s 5.22 ---- 6,775KB/s 18.86 ---- 47,349KB/s 129.89
         3. 25,929KB/s 4.93 ---- 7,378KB/s 17.32 ---- 32,350KB/s 131.88

Patched:   SYNC read            SYNC-NOIDLE read      ASYNC write  
        1. 24,000KB/s 5.32 ---- 6,942KB/s 18.39 ---- 30,860KB/s 135.95
        2. 23,678KB/s 5.40 ---- 7,274KB/s 17.58 ---- 67,432KB/s 120.44
        3. 23,004KB/s 5.55 ---- 6,621KB/s 19.30 ---- 36,536KB/s 148.64

Thanks,
Gui
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