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Road to ARM TechCon: Big.LITTLE software ain't that hard
Brian Jeff
10/9/2012 4:44 AM EDT
Software from Linaro
The key is that the application software running on top of a big.LITTLE processor is completely unmodified and unaware of the scheduling that is being handled under hood, much as application software is unaware of DVFS activity on mobile SoCs today. The other key is that the software development effort is minimized for a silicon vendor building a big.LITTLE processor, or for an OEM integrating such a processor – the work consists mainly of tuning the system parameters to appropriately handle the wide range of use cases for the device while saving the maximum energy and delivering optimum performance. This CPU migration software is available today from Linaro, and is being actively developed by multiple ARM partners.
The second flavor of the software is called big.LITTLE MP; it is a bit more complex than CPU migration, but nonetheless still leverages the existing OS power management infrastructure and limits the modifications to a relatively small kernel layer patch set. Big.LITTLE MP adds additional capability by giving the OS full visibility into the big and LITTLE cores in the system, and it modifies the kernel scheduler to allocate threads to the right-size core based on dynamically measured thread load and load history. This provides benefits over CPU migration, in the form of finer-grained scheduling of work and more flexible topologies, but does come at a cost of slightly more complexity in the kernel patches. An early version of this patch set is available and hosted at Linaro now, with monthly updates coming from ARM as we refine and tune the software. I should stress though that neither big.LITTLE MP nor CPU migration require code changes in the user space or really any input from the user. They effectively run as automatic energy-saving mechanisms, similar to the way DVFS works on mobile processors today.
At my talk at this year's ARM TechCon, I will be presenting the results from our first big.LITTLE test chip, and highlighting some of the progress we've been making with silicon lead partners on tuning big.LITTLE software to save energy while running real workloads. We started running web browsing and audio on top of Android 4.04, patched with big.LITTLE software, and we were able to measure impressive energy savings from the first weeks of our testing. Things have improved even further since then. I hope you'll attend my talk at this year's ARM TechCon to find out more.
Brian Jeff is a CPU product marketing manager for ARM based in Austin, Texas. He focuses on the power efficiency of application processor cores and multicore systems, including the Cortex-A5, the Cortex-A7, and other CPUs further down the roadmap.
Related links and articles:
Designing with ARM? Get a 10% discount on ARM TechCon 2012, Oct. 30 - Nov. 1 in Santa Clara. Click here to register for the year's biggest and best live event for the ARM community.
News and design articles:
Big.LITTLE processing with ARM Cortex-A15 & Cortex-A7
ARM TechCon to tip 'big-little' processors
ARM launches processor pack for big-little on TSMC 28-nm
ARM mulls 'big-little' scheme for graphics
The key is that the application software running on top of a big.LITTLE processor is completely unmodified and unaware of the scheduling that is being handled under hood, much as application software is unaware of DVFS activity on mobile SoCs today. The other key is that the software development effort is minimized for a silicon vendor building a big.LITTLE processor, or for an OEM integrating such a processor – the work consists mainly of tuning the system parameters to appropriately handle the wide range of use cases for the device while saving the maximum energy and delivering optimum performance. This CPU migration software is available today from Linaro, and is being actively developed by multiple ARM partners.
The second flavor of the software is called big.LITTLE MP; it is a bit more complex than CPU migration, but nonetheless still leverages the existing OS power management infrastructure and limits the modifications to a relatively small kernel layer patch set. Big.LITTLE MP adds additional capability by giving the OS full visibility into the big and LITTLE cores in the system, and it modifies the kernel scheduler to allocate threads to the right-size core based on dynamically measured thread load and load history. This provides benefits over CPU migration, in the form of finer-grained scheduling of work and more flexible topologies, but does come at a cost of slightly more complexity in the kernel patches. An early version of this patch set is available and hosted at Linaro now, with monthly updates coming from ARM as we refine and tune the software. I should stress though that neither big.LITTLE MP nor CPU migration require code changes in the user space or really any input from the user. They effectively run as automatic energy-saving mechanisms, similar to the way DVFS works on mobile processors today.
At my talk at this year's ARM TechCon, I will be presenting the results from our first big.LITTLE test chip, and highlighting some of the progress we've been making with silicon lead partners on tuning big.LITTLE software to save energy while running real workloads. We started running web browsing and audio on top of Android 4.04, patched with big.LITTLE software, and we were able to measure impressive energy savings from the first weeks of our testing. Things have improved even further since then. I hope you'll attend my talk at this year's ARM TechCon to find out more.
Brian Jeff is a CPU product marketing manager for ARM based in Austin, Texas. He focuses on the power efficiency of application processor cores and multicore systems, including the Cortex-A5, the Cortex-A7, and other CPUs further down the roadmap.
Related links and articles:
Designing with ARM? Get a 10% discount on ARM TechCon 2012, Oct. 30 - Nov. 1 in Santa Clara. Click here to register for the year's biggest and best live event for the ARM community.
News and design articles:
Big.LITTLE processing with ARM Cortex-A15 & Cortex-A7
ARM TechCon to tip 'big-little' processors
ARM launches processor pack for big-little on TSMC 28-nm
ARM mulls 'big-little' scheme for graphics
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