RFR(XXS): 8006894: G1: Number of marking threads missing from PrintFlagsFinal output

John Cuthbertson john.cuthbertson at oracle.com
Fri Jan 25 01:33:49 UTC 2013


Hi Ramki,

Thanks for looking at the change. I'll generate the output for CMS later 
tonight. From conversations with the perf team I believe CMS is OK in 
this regard.

JohnC

On 1/24/2013 5:29 PM, Srinivas Ramakrishna wrote:
> Looks good to me too. (Just out of curiosity, what happens with CMS, 
> is it correctly reported/set, or does it have the same issue -- i am 
> not suggesting fixing it given the EOL plans for CMS; just wondered. 
> Hmm, I think in CMS we directly use the flag variable, so should 
> probably report fine.)
>
> -- ramki
>
> On Thu, Jan 24, 2013 at 3:01 PM, John Cuthbertson 
> <john.cuthbertson at oracle.com <mailto:john.cuthbertson at oracle.com>> wrote:
>
>     Hi All,
>
>     Can I have a couple of volunteers look over this small change? The
>     webrev can be found at:
>     http://cr.openjdk.java.net/~johnc/8006894/webrev.0/
>     <http://cr.openjdk.java.net/%7Ejohnc/8006894/webrev.0/>
>
>     Summary:
>     When G1 calculates the number of marking threads based upon (the
>     develop-only) G1MarkingOverheadPercent or (more usually)
>     ParallelGCThreads, we weren't setting the value of ConcGCThreads.
>     As a result the output of PrintFlagsFinal would always show a zero
>     if ConcGCThreads wasn't specified on the command line:
>
>         uintx ConcGCThreads                             = 0        
>     {product}
>
>     This made it difficult for the performance team to analyze marking
>     behavior and offer advice. With this change we now get the
>     calculated number of marking threads:
>
>     Using ParallelGCThreads (default: 4):
>
>         uintx ConcGCThreads                            := 1        
>     {product}
>
>     Using G1MarkingOverheadPercent (50):
>
>         uintx ConcGCThreads                            := 2        
>     {product}
>
>     Testing:
>     Command line testing; specjvm98 and dacapo with a low IHOP value
>     (marking threshold).
>
>     Thanks,
>
>     JohnC
>
>

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