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

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Feb 18, 2011 at 02:04:18PM +0800, Gui Jianfeng wrote:
> 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

Hi Gui,

Do you also have latency numbers? I am especially interested max completion
latencies of SYNC-NOIDLE workload.

Thanks
Vivek