Re: RFR: 8187042: Events to show which objects are associated with biased object revocations

[Robin Westberg]

Thanks for the reviews Markus, Erik and David!

Filed https://bugs.openjdk.java.net/browse/JDK-8189368 
 for the improvement to add 
information on the thread currently holding the bias when it is revoked.

Best regards,
Robin

> On 16 Oct 2017, at 13:23, Markus Gronlund  wrote:
> 
> Hi Robin,
>  
> Looks good.
> 
> Thanks
> Markus
>  
> From: Robin Westberg 
> Sent: den 13 oktober 2017 16:56
> To: David Holmes
> Cc: serviceability-dev@openjdk.java.net
> Subject: Re: RFR: 8187042: Events to show which objects are associated with 
> biased object revocations
>  
> Hi again,
>  
> Here’s an updated version that adds a separate event for the self-revocation 
> path. It’s a new event class as it is a bit different from the 
> non-self-revocation path, it does not have any relevant safepoint ID for 
> example.
>  
> Webrev:
> http://cr.openjdk.java.net/~egahlin/8187042_2/ 
>  
>  
> Third, I would have expected to see more detail in the event such as which 
> thread (id) the object was biased to and which thread revoked the bias. Even 
> perhaps some notion of which instance was involved (though that's harder to 
> shows).
> Right, I’ve been looking at capturing which thread the object was biased 
> towards, but I was afraid of the possible races there as the thread pointer 
> in the mark would have to be saved before executing the VM operation. For 
> that to work 100% reliably I suspect it would have to be done inside the 
> safepoint.
> 
> Right the thread holding the bias may not even exist any more! This may need 
> to utilise the new Thread-SMR work (as a future RFE of course). :)
>  
> Ah yeah, that may be an effective way of doing it. Another idea suggested by 
> Markus Grönlund was to capture the thread’s id inside the operation and 
> propagate it through an additional field in the VM operation class. But 
> anyway, I’ll file a separate RFE for investigating that improvement.
>  
> Best regards,
> Robin
> 
> 
> I will create an updated webrev after looking into adding an event for the 
> self-revocation path.
> 
> Thanks,
> David
> 
> 
> Best regards,
> Robin

RE: RFR: 8187042: Events to show which objects are associated with biased object revocations

[Markus Gronlund]

Hi Robin,

 

Looks good.


Thanks

Markus

 

From: Robin Westberg 
Sent: den 13 oktober 2017 16:56
To: David Holmes
Cc: serviceability-dev@openjdk.java.net
Subject: Re: RFR: 8187042: Events to show which objects are associated with 
biased object revocations

 

Hi again,

 

Here’s an updated version that adds a separate event for the self-revocation 
path. It’s a new event class as it is a bit different from the 
non-self-revocation path, it does not have any relevant safepoint ID for 
example.

 

Webrev:

http://cr.openjdk.java.net/~egahlin/8187042_2/ 

 

Third, I would have expected to see more detail in the event such as which 
thread (id) the object was biased to and which thread revoked the bias. Even 
perhaps some notion of which instance was involved (though that's harder to 
shows).

Right, I’ve been looking at capturing which thread the object was biased 
towards, but I was afraid of the possible races there as the thread pointer in 
the mark would have to be saved before executing the VM operation. For that to 
work 100% reliably I suspect it would have to be done inside the safepoint.


Right the thread holding the bias may not even exist any more! This may need to 
utilise the new Thread-SMR work (as a future RFE of course). :)

 

Ah yeah, that may be an effective way of doing it. Another idea suggested by 
Markus Grönlund was to capture the thread’s id inside the operation and 
propagate it through an additional field in the VM operation class. But anyway, 
I’ll file a separate RFE for investigating that improvement.

 

Best regards,

Robin





I will create an updated webrev after looking into adding an event for the 
self-revocation path.


Thanks,
David




Best regards,
Robin

 

Re: RFR: 8187042: Events to show which objects are associated with biased object revocations

[David Holmes]

Thanks robin, these updates seem fine to me.

David

On 14/10/2017 12:56 AM, Robin Westberg wrote:

Hi again,

Here’s an updated version that adds a separate event for the 
self-revocation path. It’s a new event class as it is a bit different 
from the non-self-revocation path, it does not have any relevant 
safepoint ID for example.


Webrev:
http://cr.openjdk.java.net/~egahlin/8187042_2/

Third, I would have expected to see more detail in the event such as 
which thread (id) the object was biased to and which thread revoked 
the bias. Even perhaps some notion of which instance was involved 
(though that's harder to shows).
Right, I’ve been looking at capturing which thread the object was 
biased towards, but I was afraid of the possible races there as the 
thread pointer in the mark would have to be saved before executing 
the VM operation. For that to work 100% reliably I suspect it would 
have to be done inside the safepoint.


Right the thread holding the bias may not even exist any more! This 
may need to utilise the new Thread-SMR work (as a future RFE of 
course). :)


Ah yeah, that may be an effective way of doing it. Another idea 
suggested by Markus Grönlund was to capture the thread’s id inside the 
operation and propagate it through an additional field in the VM 
operation class. But anyway, I’ll file a separate RFE for investigating 
that improvement.


Best regards,
Robin

I will create an updated webrev after looking into adding an event 
for the self-revocation path.


Thanks,
David


Best regards,
Robin

Re: RFR: 8187042: Events to show which objects are associated with biased object revocations

[Robin Westberg]

Hi again,

Here’s an updated version that adds a separate event for the self-revocation 
path. It’s a new event class as it is a bit different from the 
non-self-revocation path, it does not have any relevant safepoint ID for 
example.

Webrev:
http://cr.openjdk.java.net/~egahlin/8187042_2/ 
 

>>> Third, I would have expected to see more detail in the event such as which 
>>> thread (id) the object was biased to and which thread revoked the bias. 
>>> Even perhaps some notion of which instance was involved (though that's 
>>> harder to shows).
>> Right, I’ve been looking at capturing which thread the object was biased 
>> towards, but I was afraid of the possible races there as the thread pointer 
>> in the mark would have to be saved before executing the VM operation. For 
>> that to work 100% reliably I suspect it would have to be done inside the 
>> safepoint.
> 
> Right the thread holding the bias may not even exist any more! This may need 
> to utilise the new Thread-SMR work (as a future RFE of course). :)

Ah yeah, that may be an effective way of doing it. Another idea suggested by 
Markus Grönlund was to capture the thread’s id inside the operation and 
propagate it through an additional field in the VM operation class. But anyway, 
I’ll file a separate RFE for investigating that improvement.

Best regards,
Robin

>> I will create an updated webrev after looking into adding an event for the 
>> self-revocation path.
> 
> Thanks,
> David
> 
>> Best regards,
>> Robin

Re: RFR: 8187042: Events to show which objects are associated with biased object revocations

[David Holmes]

Hi Robin,

On 10/10/2017 12:57 AM, Robin Westberg wrote:

Hi David,

Thanks for taking the time to look at this!


On 9 Oct 2017, at 03:26, David Holmes  wrote:

Hi Robin,

On 6/10/2017 8:22 PM, Robin Westberg wrote:

Hi all,
Please review this change to add event-based tracing events for biased lock 
revocations:
Issue: https://bugs.openjdk.java.net/browse/JDK-8187042
Webrev (courtesy of Erik Gahlin): http://cr.openjdk.java.net/~egahlin/8187042/


I have a few queries:

First, why is there no event for the self-revocation path?


That’s a good question, I did not want to add events for revocations done 
without consulting the bulk revocation heuristics (as that could generate a 
very large amount of events), so I may have mistakenly thought of the 
self-revocation as a part of that.. But certainly makes sense to have an event 
there as well, I’ll do a bit of testing and add one.


Ok.


Second, is there a reason you can't put the event management inside the VM 
operation code and so avoid the need to adjust the safepoint counter?


Well yes, the event itself is configured to record the current thread together 
with a stack trace, but that requires that the event is actually generated from 
the thread that should be recorded.


Ah - good point. And good to know the requesting thread is captured - 
that wasn't clear to me from the event snippets in the webrev.



Third, I would have expected to see more detail in the event such as which 
thread (id) the object was biased to and which thread revoked the bias. Even 
perhaps some notion of which instance was involved (though that's harder to 
shows).


Right, I’ve been looking at capturing which thread the object was biased 
towards, but I was afraid of the possible races there as the thread pointer in 
the mark would have to be saved before executing the VM operation. For that to 
work 100% reliably I suspect it would have to be done inside the safepoint.


Right the thread holding the bias may not even exist any more! This may 
need to utilise the new Thread-SMR work (as a future RFE of course). :)



I will create an updated webrev after looking into adding an event for the 
self-revocation path.


Thanks,
David


Best regards,
Robin

Re: RFR: 8187042: Events to show which objects are associated with biased object revocations

[Robin Westberg]

Hi David,

Thanks for taking the time to look at this!

> On 9 Oct 2017, at 03:26, David Holmes  wrote:
> 
> Hi Robin,
> 
> On 6/10/2017 8:22 PM, Robin Westberg wrote:
>> Hi all,
>> Please review this change to add event-based tracing events for biased lock 
>> revocations:
>> Issue: https://bugs.openjdk.java.net/browse/JDK-8187042
>> Webrev (courtesy of Erik Gahlin): 
>> http://cr.openjdk.java.net/~egahlin/8187042/
> 
> I have a few queries:
> 
> First, why is there no event for the self-revocation path?

That’s a good question, I did not want to add events for revocations done 
without consulting the bulk revocation heuristics (as that could generate a 
very large amount of events), so I may have mistakenly thought of the 
self-revocation as a part of that.. But certainly makes sense to have an event 
there as well, I’ll do a bit of testing and add one.

> Second, is there a reason you can't put the event management inside the VM 
> operation code and so avoid the need to adjust the safepoint counter?

Well yes, the event itself is configured to record the current thread together 
with a stack trace, but that requires that the event is actually generated from 
the thread that should be recorded.

> Third, I would have expected to see more detail in the event such as which 
> thread (id) the object was biased to and which thread revoked the bias. Even 
> perhaps some notion of which instance was involved (though that's harder to 
> shows).

Right, I’ve been looking at capturing which thread the object was biased 
towards, but I was afraid of the possible races there as the thread pointer in 
the mark would have to be saved before executing the VM operation. For that to 
work 100% reliably I suspect it would have to be done inside the safepoint.

I will create an updated webrev after looking into adding an event for the 
self-revocation path.

Best regards,
Robin

Re: RFR: 8187042: Events to show which objects are associated with biased object revocations

[David Holmes]

Hi Robin,

On 6/10/2017 8:22 PM, Robin Westberg wrote:

Hi all,

Please review this change to add event-based tracing events for biased 
lock revocations:


Issue: https://bugs.openjdk.java.net/browse/JDK-8187042
Webrev (courtesy of Erik Gahlin): 
http://cr.openjdk.java.net/~egahlin/8187042/


I have a few queries:

First, why is there no event for the self-revocation path?

Second, is there a reason you can't put the event management inside the 
VM operation code and so avoid the need to adjust the safepoint counter?


Third, I would have expected to see more detail in the event such as 
which thread (id) the object was biased to and which thread revoked the 
bias. Even perhaps some notion of which instance was involved (though 
that's harder to shows).


Thanks,
David


Best regards,
Robin

Re: RFR: 8187042: Events to show which objects are associated with biased object revocations

[Erik Gahlin]

Looks good!

Erik


> On 6 Oct 2017, at 12:22, Robin Westberg  wrote:
> 
> Hi all,
> 
> Please review this change to add event-based tracing events for biased lock 
> revocations:
> 
> Issue: https://bugs.openjdk.java.net/browse/JDK-8187042 
> 
> Webrev (courtesy of Erik Gahlin): 
> http://cr.openjdk.java.net/~egahlin/8187042/ 
> 
> 
> Best regards,
> Robin

RE: RFR: 8187042: Events to show which objects are associated with biased object revocations

[Markus Gronlund]

Hi Robin,

 

This looks good, thank you very much for adding this!

 

Cheers

Markus

 

From: Robin Westberg 
Sent: den 6 oktober 2017 12:22
To: serviceability-dev@openjdk.java.net
Subject: RFR: 8187042: Events to show which objects are associated with biased 
object revocations

 

Hi all,

 

Please review this change to add event-based tracing events for biased lock 
revocations:

 

Issue: https://bugs.openjdk.java.net/browse/JDK-8187042

Webrev (courtesy of Erik Gahlin): http://cr.openjdk.java.net/~egahlin/8187042/

 

Best regards,

Robin

RFR: 8187042: Events to show which objects are associated with biased object revocations

[Robin Westberg]

Hi all,

Please review this change to add event-based tracing events for biased lock 
revocations:

Issue: https://bugs.openjdk.java.net/browse/JDK-8187042 

Webrev (courtesy of Erik Gahlin): http://cr.openjdk.java.net/~egahlin/8187042/ 


Best regards,
Robin