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Re: [PATCH v6 00/12] *** A Method for evaluating dirty page rate ***
From: |
David Edmondson |
Subject: |
Re: [PATCH v6 00/12] *** A Method for evaluating dirty page rate *** |
Date: |
Mon, 31 Aug 2020 11:08:45 +0100 |
On Monday, 2020-08-31 at 17:55:39 +08, Zheng Chuan wrote:
> On 2020/8/31 17:05, David Edmondson wrote:
>> Trying to think like a control plane developer and user (of which I am
>> neither) raised some questions about the overall interface provided
>> here. If everyone else is happy with the current interface, then I'll
>> shut up :-)
>>
>> It seems like it should be possible to query the last measured dirty
>> rate at any time. In particular, it should be possible to query the
>> value before any rate has been measured (either returning an error, or
>> if that is unpalatable perhaps a result with a zero interval to indicate
>> "this data isn't useful"), but also *during* a subsequent measurement
>> period.
>>
> Hi, Thank you for your review.
>
> For now,
> i. if we query the value before any rate has been measured, it will return
> unstarted,
> and dirtyrate will return -1.
> {"return":{"status":"unstarted","dirty-rate":-1,"start-time":0,"calc-time":0},"id":"libvirt-14"}
>
> ii.if we specify the measurement interval like -1 or 61, it will return error
> {"id":"libvirt-13","error":{"class":"GenericError","desc":"calc-time is out
> of range[1, 60]."}}
>
> iii. We can query the last measured dirty rate at any time now as you
> expected in last patch version
> with returning the measurement timestamp and calc-time.
>
> If i have missed some other scenes, please let me know:)
No, I think that you have everything. My aim was to see if other people
agreed with the usage scenarios.
>> That is, the result of the previous measurement should always be
>> available on demand and a measurement becomes "current" when it
>> completes.
>>
>> Given that we allow the caller to specify the measurement interval, some
>> callers might specify a long period. As only one measurement can be
>> taken at a time, a long running measurement rules out taking a short
>> measurement. That's probably okay, but does lead me to wonder whether
>> the API should include a mechanism allowing the cancellation of an
>> in-progress measurement.
>
> That's why we restrict the maximum time to 60s, i think this is enough and
> also
> not too long for user to observe the average dirty rate.
> I think it is may a little expensive and hardly used to implement
> cancellation mechanism.
>
> On the other hand, users could call several times with the measurement
> interval
> like 1s, to improve its accuracy otherwise observe a long time.
Understood.
dme.
--
Modern people tend to dance.
- Re: [PATCH v6 08/12] migration/dirtyrate: skip sampling ramblock with size below MIN_RAMBLOCK_SIZE, (continued)
- [PATCH v6 05/12] migration/dirtyrate: move RAMBLOCK_FOREACH_MIGRATABLE into ram.h, Chuan Zheng, 2020/08/28
- [PATCH v6 07/12] migration/dirtyrate: Compare page hash results for recorded sampled page, Chuan Zheng, 2020/08/28
- [PATCH v6 12/12] migration/dirtyrate: Add trace_calls to make it easier to debug, Chuan Zheng, 2020/08/28
- [PATCH v6 11/12] migration/dirtyrate: Implement qmp_cal_dirty_rate()/qmp_get_dirty_rate() function, Chuan Zheng, 2020/08/28
- Re: [PATCH v6 00/12] *** A Method for evaluating dirty page rate ***, David Edmondson, 2020/08/31