RFR: 8069273: Decrease Hot Card Cache Lock contention

[Claes Redestad]

Mikael,

On 01/27/2015 02:56 PM, Mikael Gerdin wrote:
> Hi Claes,
>
> On 2015-01-27 11:32, Claes Redestad wrote:
>> Hi again,
>>
>> new webrev: http://cr.openjdk.java.net/~redestad/8069273/webrev.04/
>
> The change looks good to me.

Thanks!

/Claes

>
> /Mikael
>
>>
>> This version fixes a crash issue in G1HotCardCache::reset_hot_cache when
>> G1ConcRSLogCacheSize=0
>>
>> G1HotCardCache::hot_cache_is_empty was broken in the same way, but
>> since it was unused I've opted to remove it rather than fix it.
>>
>> /Claes
>>
>> On 01/23/2015 04:34 PM, Claes Redestad wrote:
>>> Hi all,
>>>
>>> updated webrev: http://cr.openjdk.java.net/~redestad/8069273/webrev.02/
>>>
>>> Changes: after some helpful suggestions offline from Stefan Karlsson 
>>> I've
>>> replaced the cmpxchg loop on _hot_cache_idx with use of Atomic::add.
>>> This is arguably cleaner and also improves performance dramatically on
>>> architectures with support for atomic adds.
>>>
>>> /Claes
>>>
>>> On 01/22/2015 05:27 PM, Claes Redestad wrote:
>>>> Hi all,
>>>>
>>>> please review this patch which replaces the use of mutex-based
>>>> locking in
>>>> G1HotCardCache with a non-blockingCAS loop.
>>>>
>>>> webrev: http://cr.openjdk.java.net/~redestad/8069273/webrev.01/
>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8069273
>>>>
>>>> This improves performance in a microbenchmark designed to indirectly
>>>> stress the "card is hot" branch of G1HotCardCache::insert[1]. More
>>>> thorough
>>>> performance testing is in progress.
>>>>
>>>> An initial prototype did not isolate the _hot_cache_idx, which
>>>> introduced
>>>> catastrophic levels of false sharing on nearby fields, ending up in
>>>> odd results and no real effect on total throughput. The padding
>>>> introduced
>>>> around_hot_cache_idx and _hot_cache_par_claimed_idx was necessary to
>>>> address this.
>>>>
>>>> Testing: JPRT -testset hotspot
>>>>
>>>> /Claes
>>>>
>>>> [1] http://cr.openjdk.java.net/~redestad/8069273/G1HotCardBench.java
>>>
>>