"Jason J. Herne" <jjhe...@linux.vnet.ibm.com> wrote:
> On 06/02/2015 09:58 AM, Dr. David Alan Gilbert wrote:
>> * Jason J. Herne (jjhe...@linux.vnet.ibm.com) wrote:
>>> On 06/01/2015 11:32 AM, Dr. David Alan Gilbert wrote:
>>>> * Jason J. Herne (jjhe...@linux.vnet.ibm.com) wrote:
>>>>> Remove traditional auto-converge static 30ms throttling code and replace
>>>>> it
>>>>> with a dynamic throttling algorithm.
>>>>>
>>>>> Additionally, be more aggressive when deciding when to start throttling.
>>>>> Previously we waited until four unproductive memory passes. Now we begin
>>>>> throttling after only two unproductive memory passes. Four seemed quite
>>>>> arbitrary and only waiting for two passes allows us to complete the
>>>>> migration
>>>>> faster.
>>>>>
>>>>> Signed-off-by: Jason J. Herne <jjhe...@linux.vnet.ibm.com>
>>>>> Reviewed-by: Matthew Rosato <mjros...@linux.vnet.ibm.com>
>>>>> ---
>>>>> arch_init.c | 95
>>>>> +++++++++++++++++----------------------------------
>>>>> migration/migration.c | 9 +++++
>>>>> 2 files changed, 41 insertions(+), 63 deletions(-)
>>>>>
>>>>> diff --git a/arch_init.c b/arch_init.c
>>>>> index 23d3feb..73ae494 100644
>>>>> --- a/arch_init.c
>>>>> +++ b/arch_init.c
>>>>> @@ -111,9 +111,7 @@ int graphic_depth = 32;
>>>>> #endif
>>>>>
>>>>> const uint32_t arch_type = QEMU_ARCH;
>>>>> -static bool mig_throttle_on;
>>>>> static int dirty_rate_high_cnt;
>>>>> -static void check_guest_throttling(void);
>>>>>
>>>>> static uint64_t bitmap_sync_count;
>>>>>
>>>>> @@ -487,6 +485,31 @@ static size_t save_page_header(QEMUFile *f, RAMBlock
>>>>> *block, ram_addr_t offset)
>>>>> return size;
>>>>> }
>>>>>
>>>>> +/* Reduce amount of guest cpu execution to hopefully slow down memory
>>>>> writes.
>>>>> + * If guest dirty memory rate is reduced below the rate at which we can
>>>>> + * transfer pages to the destination then we should be able to complete
>>>>> + * migration. Some workloads dirty memory way too fast and will not
>>>>> effectively
>>>>> + * converge, even with auto-converge. For these workloads we will
>>>>> continue to
>>>>> + * increase throttling until the guest is paused long enough to complete
>>>>> the
>>>>> + * migration. This essentially becomes a non-live migration.
>>>>> + */
>>>>> +static void mig_throttle_guest_down(void)
>>>>> +{
>>>>> + CPUState *cpu;
>>>>> +
>>>>> + CPU_FOREACH(cpu) {
>>>>> + /* We have not started throttling yet. Lets start it.*/
>>>>> + if (!cpu_throttle_active(cpu)) {
>>>>> + cpu_throttle_start(cpu, 0.2);
>>>>> + }
>>>>> +
>>>>> + /* Throttling is already in place. Just increase the throttling
>>>>> rate */
>>>>> + else {
>>>>> + cpu_throttle_start(cpu, cpu_throttle_get_ratio(cpu) * 2);
>>>>> + }
>>>>
>>>> Now that migration has migrate_parameters, it would be best to replace
>>>> the magic numbers (the 0.2, the *2 - anything else?) by parameters that
>>>> can
>>>> change the starting throttling and increase rate. It would probably also
>>>> be
>>>> good to make the current throttling rate visible in info somewhere; maybe
>>>> info migrate?
>>>>
>>>
>>> I did consider all of this. However, I don't think that the controls
>>> this patch provides are an ideal throttling mechanism. I suspect someone
>>> with
>>> vcpu/scheduling experience could whip up something more user friendly and
>>> cleaner.
>>> I merely propose this because it seems better than what we have today for
>>> auto-converge.
>>>
>>> Also, I'm not sure how useful the information really is to the user. The
>>> fact that it is a ratio instead of a percentage might be confusing. Also,
>>> I suspect it is not
>>> truly very accurate. Again, I was going for "make it better", not "make it
>>> perfect".
>>>
>>> Lastly, if we define this external interface we are kind of stuck with it,
>>> yes?
>>
>> Well, one thing you can do is add a parameter with a name starting with x-
>> which means it's not a fixed interface (so things like libvirt wont use it).
>> And the reason I was interested in seeing the information was otherwise
>> we don't really have any way of knowing how well the code is working;
>> is it already throttling down more and more?
>>
>
> Fair point. Can we add a qmp/hmp command like "info x-cpu-throttle"? Or a
> new line in "info migrate" output, "x-throttle-ration: 1.0" perhaps?
> Would this mess up libvirt's parsing of the hmp/qmp data?
info migrate with extra field, please. Name it with x-throotle-ratio or
whatever.
I would also preffer to ha a percentage (or per thousand) that is an
integer, but that is just a prefference and I don't really care too
much.
Later, Juan.
