Re: [Qemu-devel] [PATCH v8 3/3] Force auto-convegence of live migration

[Chegu Vinod <chegu_vinod@hp.com>]

On 6/24/2013 8:59 AM, Paolo Bonzini wrote:
> Il 24/06/2013 11:47, Chegu Vinod ha scritto:
>> If a user chooses to turn on the auto-converge migration capability
>> these changes detect the lack of convergence and throttle down the
>> guest. i.e. force the VCPUs out of the guest for some duration
>> and let the migration thread catchup and help converge.
>>
>> Verified the convergence using the following :
>>   - Java Warehouse workload running on a 20VCPU/256G guest(~80% busy)
>>   - OLTP like workload running on a 80VCPU/512G guest (~80% busy)
>>
>> Sample results with Java warehouse workload : (migrate speed set to 20Gb and
>> migrate downtime set to 4seconds).
>>
>>   (qemu) info migrate
>>   capabilities: xbzrle: off auto-converge: off  <----
>>   Migration status: active
>>   total time: 1487503 milliseconds
>>   expected downtime: 519 milliseconds
>>   transferred ram: 383749347 kbytes
>>   remaining ram: 2753372 kbytes
>>   total ram: 268444224 kbytes
>>   duplicate: 65461532 pages
>>   skipped: 64901568 pages
>>   normal: 95750218 pages
>>   normal bytes: 383000872 kbytes
>>   dirty pages rate: 67551 pages
>>
>>   ---
>>
>>   (qemu) info migrate
>>   capabilities: xbzrle: off auto-converge: on   <----
>>   Migration status: completed
>>   total time: 241161 milliseconds
>>   downtime: 6373 milliseconds
>>   transferred ram: 28235307 kbytes
>>   remaining ram: 0 kbytes
>>   total ram: 268444224 kbytes
>>   duplicate: 64946416 pages
>>   skipped: 64903523 pages
>>   normal: 7044971 pages
>>   normal bytes: 28179884 kbytes
>>
>> Signed-off-by: Chegu Vinod <chegu_vinod@hp.com>
> As far as the algorithm is concerned,
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks!
>
> but are you sure that this passes checkpatch.pl?

Yes it does (had checked it before I posted).

# ./scripts/checkpatch.pl 
0003-Force-auto-convegence-of-live-migration.patch
total: 0 errors, 0 warnings, 114 lines checked

0003-Force-auto-convegence-of-live-migration.patch has no obvious style 
problems and is ready for submission.

Vinod
>
>> +            /* The following detection logic can be refined later. For now:
>> +               Check to see if the dirtied bytes is 50% more than the approx.
>> +               amount of bytes that just got transferred since the last time we
>> +               were in this routine. If that happens >N times (for now N==4)
>> +               we turn on the throttle down logic */
>> +            bytes_xfer_now = ram_bytes_transferred();
>> +            if (s->dirty_pages_rate &&
>> +               (num_dirty_pages_period * TARGET_PAGE_SIZE >
>> +                   (bytes_xfer_now - bytes_xfer_prev)/2) &&
>> +               (dirty_rate_high_cnt++ > 4)) {
> the spacing of the operators here looks like something checkpatch.pl
> would complain about.  If you have to respin for that, keep my R-b and
> please also remove all other superfluous parentheses.
>
> Paolo
>
>> +                    trace_migration_throttle();
>> +                    mig_throttle_on = true;
>> +                    dirty_rate_high_cnt = 0;
>> +             }
>> +             bytes_xfer_prev = bytes_xfer_now;
>> +        } else {
>> +             mig_throttle_on = false;
>> +        }
>>           s->dirty_pages_rate = num_dirty_pages_period * 1000
>>               / (end_time - start_time);
>>           s->dirty_bytes_rate = s->dirty_pages_rate * TARGET_PAGE_SIZE;
>> @@ -566,6 +592,8 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>>       migration_bitmap = bitmap_new(ram_pages);
>>       bitmap_set(migration_bitmap, 0, ram_pages);
>>       migration_dirty_pages = ram_pages;
>> +    mig_throttle_on = false;
>> +    dirty_rate_high_cnt = 0;
>>   
>>       if (migrate_use_xbzrle()) {
>>           XBZRLE.cache = cache_init(migrate_xbzrle_cache_size() /
>> @@ -628,6 +656,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
>>           }
>>           total_sent += bytes_sent;
>>           acct_info.iterations++;
>> +        check_guest_throttling();
>>           /* we want to check in the 1st loop, just in case it was the 1st time
>>              and we had to sync the dirty bitmap.
>>              qemu_get_clock_ns() is a bit expensive, so we only check each some
>> @@ -1097,3 +1126,53 @@ TargetInfo *qmp_query_target(Error **errp)
>>   
>>       return info;
>>   }
>> +
>> +/* Stub function that's gets run on the vcpu when its brought out of the
>> +   VM to run inside qemu via async_run_on_cpu()*/
>> +static void mig_sleep_cpu(void *opq)
>> +{
>> +    qemu_mutex_unlock_iothread();
>> +    g_usleep(30*1000);
>> +    qemu_mutex_lock_iothread();
>> +}
>> +
>> +/* To reduce the dirty rate explicitly disallow the VCPUs from spending
>> +   much time in the VM. The migration thread will try to catchup.
>> +   Workload will experience a performance drop.
>> +*/
>> +static void mig_throttle_cpu_down(CPUState *cpu, void *data)
>> +{
>> +    async_run_on_cpu(cpu, mig_sleep_cpu, NULL);
>> +}
>> +
>> +static void mig_throttle_guest_down(void)
>> +{
>> +    qemu_mutex_lock_iothread();
>> +    qemu_for_each_cpu(mig_throttle_cpu_down, NULL);
>> +    qemu_mutex_unlock_iothread();
>> +}
>> +
>> +static void check_guest_throttling(void)
>> +{
>> +    static int64_t t0;
>> +    int64_t        t1;
>> +
>> +    if (!mig_throttle_on) {
>> +        return;
>> +    }
>> +
>> +    if (!t0)  {
>> +        t0 = qemu_get_clock_ns(rt_clock);
>> +        return;
>> +    }
>> +
>> +    t1 = qemu_get_clock_ns(rt_clock);
>> +
>> +    /* If it has been more than 40 ms since the last time the guest
>> +     * was throttled then do it again.
>> +     */
>> +    if (40 < (t1-t0)/1000000) {
>> +        mig_throttle_guest_down();
>> +        t0 = t1;
>> +    }
>> +}
>>
> .
>