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From Alexei Fedotov <alexei.fedo...@gmail.com>
Subject Re: [classlib] Fixing an unsafe reference in InputStream
Date Mon, 16 Nov 2009 11:01:09 GMT
I support reluctance in fixing performance. AFAIK, no performance
change should be done without demonstrating incerase on real loads.

2009/11/13 Tim Ellison <t.p.ellison@gmail.com>:
> On 12/Nov/2009 19:20, Vijay Menon wrote:
>> Right, writes - even unsynchronized ones - to the same cache line are
>> problematic.  Here's a good quick read on this:
>> http://en.wikipedia.org/wiki/MESI_protocol.  Recent Intel architectures
>> adapt this protocol.  Here's the interesting bit:
>>
>> A write may only be performed if the cache line is in the Modified or
>> Exclusive state. If it is in the Shared state, all other cached copies must
>> be invalidated first. This is typically done by a broadcast operation known
>> as *Read For Ownership (RFO)*.
>>
>>
>> If two cores continually write to the same cache line, they'll repeatedly
>> invalidate each other.
>
> Thanks for the pointers.
>
> Given that the current code has been there since time immemorial and is
> not broken, I'm inclined to leave it for now and pick this thread up
> again after M12.  That'll give us time to see what the difference is
> between the local and static versions (though if I were a betting person
> I'd say skip is used infrequently enough that nobody's app will notice).
>
> Regards,
> Tim
>



-- 
With best regards / с наилучшими пожеланиями,
Alexei Fedotov / Алексей Федотов,
http://www.telecom-express.ru/
http://harmony.apache.org/
http://www.expressaas.com/
http://openmeetings.googlecode.com/

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