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

[Vivek Goyal]

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.

Thanks
Vivek
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