RFR (S): 8155230: Tune thread usage for mark bitmap clear

[Jon Masamitsu]

Thomas,

Change looks good.

For the sake of future generations maybe a comment such as

  611 class G1ClearBitMapTask : public AbstractGangTask {
612 public: // A chunk size of 1M was determined empirically to be a reasonable size.

  613 static size_t chunk_size() { return M; }

Jon

On 04/28/2016 04:15 AM, Thomas Schatzl wrote:
> Hi all,
>
>    during testing of 8077144 I found that mark bitmap clearing can be
> significantly sped up by not using that many threads.
>
> A good conservative estimate (tends to use too many threads) that still
> cuts mark bitmap clear time by >50% is to give each thread at least 1
> MB of data to clear.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8155230
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8155230/webrev/
> Testing:
> jprt, webrev, various performance tests
>
> Depends on 8155232.
>
> Thanks,
>    Thomas
>

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