Re: [PATCH v3 7/7] migration/dirtyrate: implement dirty-ring dirtyrate calculation

[Hyman Huang]

在 2021/6/10 2:17, Peter Xu 写道:
> On Mon, Jun 07, 2021 at 09:15:20AM +0800, huangy81@chinatelecom.cn wrote:
> > +static void calculate_dirtyrate_vcpu(struct DirtyRateConfig config)
> > +{
> > +    CPUState *cpu;
> > +    int64_t msec = 0;
> > +    int64_t start_time;
> > +    uint64_t dirtyrate = 0;
> > +    uint64_t dirtyrate_sum = 0;
> > +    int nvcpu = 0;
> > +    int i = 0;
> > +
> > +    CPU_FOREACH(cpu) {
> > +        nvcpu++;
> > +    }
> > +
> > +    dirty_pages = g_malloc0(sizeof(*dirty_pages) * nvcpu);
> > +
> > +    dirtyrate_global_dirty_log_start();
> > +
> > +    CPU_FOREACH(cpu) {
> > +        record_dirtypages(cpu, true);
> > +    }
> > +
> > +    DirtyStat.method.vcpu.nvcpu = nvcpu;
> > +    if (last_method != CALC_DIRTY_RING) {
> > +        DirtyStat.method.vcpu.rates =
> > +            g_malloc0(sizeof(DirtyRateVcpu) * nvcpu);
> > +    }
> > +
> > +    start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> > +    DirtyStat.start_time = start_time / 1000;
> > +
> > +    msec = config.sample_period_seconds * 1000;
> > +    msec = set_sample_page_period(msec, start_time);
> > +    DirtyStat.calc_time = msec / 1000;
> > +
> > +    CPU_FOREACH(cpu) {
> > +        record_dirtypages(cpu, false);
> > +    }
> > +
> > +    dirtyrate_global_dirty_log_stop();
> > +
> > +    for (i = 0; i < DirtyStat.method.vcpu.nvcpu; i++) {
> > +        dirtyrate = do_calculate_dirtyrate_vcpu(i);
> > +        DirtyStat.method.vcpu.rates[i].id = i;
> > +        DirtyStat.method.vcpu.rates[i].dirty_rate = dirtyrate;
> > +        dirtyrate_sum += dirtyrate;
> > +    }
> > +
> > +    DirtyStat.dirty_rate = dirtyrate_sum / DirtyStat.method.vcpu.nvcpu;
>
> Why you'd like to divide with nvcpu?  Isn't dirtyrate_sum exactly what we want?
> As I don't think we care about average per-vcpu dirty rate, but total here.
the initial idea of mine is that the qmp output dirty rate represent the 
average dirty rate, my mistake.indeed, the vm dirty rate should not be 
the average of vcpu's, i'll fix it the next version.
> > +    g_free(dirty_pages);
> > +}
>
> I did a run with 4G mem VM, alloc 1G and dirty it with 500MB/s, then
>
>    - With old way: I got 95MB/s
>    - With new way: I got 128MB/s
>
> The new way has the output with:
>
> Dirty rate: 128 (MB/s)
> vcpu[0], Dirty rate: 0
> vcpu[1], Dirty rate: 1
> vcpu[2], Dirty rate: 0
> vcpu[3], Dirty rate: 511
>
> I think if without the division, it'll be 512MB/s, which is matching the dirty
> workload I initiated.

--
Best regard

Hyman Huang(黄勇)