[PATCH 1/5] drm/i915/gvt: add some statistic routine for scheduler

[Du, Changbin]

On Tue, Feb 07, 2017 at 08:53:01AM +0800, Gao, Ping A wrote:
> 
> On 2017/2/6 14:30, Du, Changbin wrote:
> > On Thu, Jan 26, 2017 at 09:19:14AM +0800, Ping Gao wrote:
> >> Add some statistic routine to collect the time when vGPU
> >> schedule in/out.
> >>
> >> Signed-off-by: Ping Gao <ping.a.gao at intel.com>
> >> ---
> >>
> >> @@ -77,6 +99,14 @@ static void try_to_schedule_next_vgpu(struct intel_gvt *gvt)
> >>  	gvt_dbg_sched("switch to next vgpu %d\n",
> >>  			scheduler->next_vgpu->id);
> >>  
> >> +	cur_cycles = get_cycles();
> >> +	if (scheduler->current_vgpu) {
> >> +		vgpu_data = scheduler->current_vgpu->sched_data;
> >> +		vgpu_data->sched_out_time = cur_cycles;
> >> +	}
> >> +	vgpu_data = scheduler->next_vgpu->sched_data;
> >> +	vgpu_data->sched_in_time = cur_cycles;
> >> +
> >>  	/* switch current vgpu */
> >>  	scheduler->current_vgpu = scheduler->next_vgpu;
> >>  	scheduler->next_vgpu = NULL;
> > Hi, Ping. I am thinking whether jiffies has good resolution here,
> > because the schedule period is as long as 100ms. 
> > As you know the TSC has many issues today, considring its behaviour
> > varies from different CPUs. It turns out TSC is hard to use to
> > measure time. Though recent intel CPU has a constant TSC, but to
> > keep code compatibility a more common time source should be prefered.
> 
> Hi Changbin, The default schedule period should set to 1ms, as most ctx
> finished in 2ms;
> jiffies is not suitable for this purpose:
> 1. jiffies is not precise enough, as ctx executing time is varied from
> hundred nanosecond to several microsecond.
> 2. it depend on the HZ of the system setting, vGPU scheduler behavior
> should not rely on any config setting.
> 
oh, jiffies only has microsecond resolution. Hence seems only tsc can
meet this requirment. I think you can add a inline function like
tsc2ns(). :)

> >> -- 
> >> 2.7.4
> >>
> >> _______________________________________________
> >> intel-gvt-dev mailing list
> >> intel-gvt-dev at lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev
> 
> _______________________________________________
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> intel-gvt-dev at lists.freedesktop.org
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-- 
Best Regards,
Open Source Technology Center, Intel Corp.
Du, Changbin
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