Relevance of Quad Core processors in mobile computing

October edition of EE Times Europe has an article written by +Marco Cornero from ST Ericsson explaining how Quad core processors for mobile computing is ahead of its time. The following tweet was send from the official ST Ericsson account.

“Quad cores in mobile platforms: Is the time right?” An article in EETimes Europe written by Marco Cornero, ST-Ericsson http://ow.ly/6TrDo

Please note that you might need to log in to EE Times website to access the full article along with the whole October edition.

In some ways this is quite a brazen stance taken by ST Ericsson.

1. +Marco Cornero states that there is a 25% to 30% performance overhead on each core while moving from Dual to Quad, this is due to systemic latency attributed to L1/L2 cache synchronization, bus access etc.

2. This overhead will mandate that for a Quad core to out perform Dual core each software application needs to have 70% of its code capable of executing in parallel. How this is calculated is clearly explained in the article.

The article also argues that there are not many complex use cases which can create multi-tasking scenarios where there is optimal usage of all the four cores and multiple other arguments which seems to conclusively prove that Quad cores is a case of “Diminishing returns” (See below quote from ST Ericsson CEO Mr.Gilles Delfassy)

“We aim to be leaders in apps processors, but there is a big debate whether quad core is a case of diminishing returns,” – Gilles Delfassy

The whole Article hinges on one fact that there will be a 25%-30% performance overhead on each core while moving from Dual to Quad, but isn’t this purely dependent on hardware? This figure may hold good for ST Ericsson chip-set, but what about ASICs from Qualcomm, NVIDIA, Marvel etc?

The crux of the argument is this very overhead percentage and if we bring this overhead marginally down to 20-25%, then only 50-60% of the application code needs to execute in parallel for optimal usage of Quad core. This situation is not so bad. Is this inference inherently flawed? The fact that Qualcomm and NVIDIA are close to bringing out Quad core solutions to market makes me wonder about ST Ericsson’s claims!

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