It might seem silly to point out that SoCs, System-on-Chips, don't simply arrive at a smartphone manufacturer in a box and are soldered into the circuit board somewhere along a production line. Instead, the process includes designing, licensing, testing, integrating and selling the SoCs into the chassis takes many months. As part of the process, the SoC manufacturer usually releases several different versions of a given System-on-Chip. This is nothing new: typically, the first version that manufacturers get their hands on is version 1 and this is produced in "engineering sample" quantities. In other words, it's designed as a pre-production unit and is subject to improvements. Qualcomm's Snapdragon 810 is no different - the early pre-production 810s have a reputation for running very hot and had memory manager issues. Putting aside Qualcomm's confusing denial of heating issues with the 810, by the time the processor made it into production devices it was already at version 2. This is the processor that's been used in a number of different devices including the HTC One M9 and LG G Flex 2. And unfortunately, these devices have a reputation for running hot, but it turns out that Qualcomm have released a numerically minor revision to the Snapdragon 810 and the later model has a number of thermal improvements. So far, we know that the Xiaomi Mi Note Pro uses the 810 version 2.1.
At this time, Qualcomm have not detailed the changes between the Snapdragon 810 v2 and v2.1, but thanks to Anandtech and OnePlus we have details of a number of the changes. The first change is a small increase in the Adreno 430's maximum clock speed from 600 MHz to 630 MHz. In line with this 5% increase in clock speed, the GPU now runs around 5% quicker, very much as expected. Another difference is how the Snapdragon 810 performs when handling memory activity. Tests showed that memory latency (that is, how quick cache and main memory is to respond to requests) is faster by a handful of nanoseconds, but memory bandwidth is increased by more than a third. This should have a knock on effect on the device running the 2.1 version of the processor as it could help smooth multitasking when working with large data or application files.
Anandtech also discovered that Qualcomm have changed how the Snapdragon 810 performs and how aggressively the processor throttles the A57 cores when under load, which appears to be backed up with additional information from OnePlus. It's worth a quick recap as to what, exactly, this means and it's centered around how the SoC manages a blend of performance and temperature. Essentially, the Snapdragon 810 is an efficient processor but has the ability to consume a considerable amount of energy when running at full load. Under full load each individual ARM Cortex-A57 processor core can consume over 4w of energy and of course, there are four of these plus the additional four ARM Cortex-A53 cores. This electrical energy is converted into heat, which must be removed from the chassis. The more cramped the chassis, the warmer things tend to get, which is why tablets tend to outperform smartphones under similar testing. When temperatures start to climb too high, the SoC will underclock the processor in order to use less energy and so produce less heat. This reduces SoC performance and heat output.
Anandtech's testing shows that the Cortex-A57 cores are underclocked less often with revision 2.1 of the 810 compared with v2. This may be because of improvements in how the processor handles processor load and perhaps there's a clue in the OnePlus' announcement that they are using the Qualcomm Snapdragon 810 in the new OnePlus Two. OnePlus' blog states that: "We [have] worked very closely with Qualcomm's engineers to integrate an improved version of the chipset (v2.1) in the OnePlus 2, and fine-tuned both hardware and software, [respectively]." This has included using a layer of thermal gel and graphite inside the 'phone to improve chassis cooling plus additional space inside the 'phone. Additionally, the OnePlus Two's OxygenOS software is able to know what processor core should be used for a given task and will avoid using two or more cores that are adjacent to one another.
The chassis improvements will help mitigate the impact of a processor able to pump out 12 watts of heat energy in something that sits in the palm of our hand, but many readers might be thinking that OnePlus and Qualcomm's efforts are simply deferring the inevitable slowdown of the SoC thanks to heat. And yes, Andandtech discovered that the 810 v2.1 still had to disable the A57 cores in preference to the A53, however it is important to remember how most smartphone and application use the hardware: engineers use a "sprint and drift," or "race to idle" technique. A processor core will complete a given task as quickly as possible so that it may then be shut down, because when idle, most smartphone components consume next to no energy. This means that in a typical situation, we might expect the 810 to produce more heat but for a shorter period of time compared with older chipsets such as the Snapdragon 801, which produce less heat over a longer period. This means that the chassis must cope with a rather lumpy heat output from the SoC, depending on what the customer is doing.
Of course, the Snapdragon 810 is still built on a 20nm die size compared with the Samsung Exynos 7420's 14nm, which means it still requires high voltages in order to be driven. It is likely to use more energy and produce more heat than the Samsung SoC, but Samsung is currently unable or unwilling to make enough of the Exynos 7420 processor to be able to sell the to third parties. It appears Qualcomm's improvements could see the Snapdragon 810 adopted by more manufacturers until the Snapdragon 820 is released.