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A Word On Overclocking Llano

AMD A8-3850 Review: Llano Rocks Entry-Level Desktops
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Llano goes heavy on integration. AMD purposely locked clock multipliers up and down the family. And yet the company suggests you can get 30%-better 3DMark Vantage scores by cranking the reference clock up to 133 MHz and dropping the multiplier (you can go down, but not up). Because the platform’s clock generator is integrated (like Intel’s P67/H67/Z68), though, messing with the reference frequency also overclocks the northbridge, graphics core, and PCI Express bus.

The latest version of CPU-Z at stock clocksThe latest version of CPU-Z at stock clocks

Well, the faster northbridge is fairly resilient, and you can use memory dividers to bring your RAM back down into spec. Moreover, the faster graphics core is actually a welcome speed-up—that’s how you’ll end up with better frame rates in games. But the overclocked PCIe bus can be a problem.

I spent a couple of late nights chatting back and forth with the fine folks at ASRock and Gigabyte, who helped in near real-time with BIOS builds. Eventually, I was able to get Gigabyte’s A75M-UD2H dialed in at nearly 3.4 GHz (it’d run in excess of that, but crashed under load) using a 23.5x multiplier and 145 MHz reference clock reflected as 143.5 MHz. The APU only needed a .05 V bump to achieve those numbers, too.

A8-3850 overclocked to nearly 3.4 GHz on Gigabyte's A75M-UD2HA8-3850 overclocked to nearly 3.4 GHz on Gigabyte's A75M-UD2H

The problem was that I couldn’t use an SSD. Anywhere over a 110 MHz reference clock and the SSD simply ceased to be detected by the board’s BIOS. Even with a hard drive installed it’d sometimes take three or four reboots for the firmware to detect my disk. This is a known behavior Gigabyte is trying to mitigate, but it’s symptomatic of pushing clock rates system-wide beyond-spec. ASRock had a different issue with the elevated reference clock: losing USB 3.0 functionality. Other boards simply wouldn’t overclock well at all, failing long before we were forced to fight a bus speed idiosyncrasy.   

Pushing the A8-3850’s four cores from 2.9 GHz to 3.4 GHz is sure to benefit performance in processor-bound benchmarks, but it didn’t do nearly as much for gaming as simply installing faster  memory.

At the end of the day, overclocking Llano is like slapping an intake on a Ford Fiesta. You’re not buying the thing for its potential on the track. You’re getting it because it’s inexpensive and “fast enough” to serve as a capable daily driver.  

The idea of setting integrated graphics world records is humorous not because I’m a pretentious jerk, but because you could buy a Phenom II X3 720 Black Edition for $70 and a 1 GB Radeon HD 6570 for $70 and get better graphics performance right out of the box, in addition to an unlocked CPU sporting 6 MB of shared L3 cache. If you’re an overclocker, that could very well be the route to take. Llano is all about something else entirely.

Is There A Future In Llano-Based Overclocking?

Several of the boards I tested had fields for higher multiplier settings and adjustable graphics clocks. Of course, turning those knobs doesn’t actually do anything on an APU with locked ratios. So why the heck are those settings exposed?

According to my sources, AMD plans to sell a Black Edition APU based on the Llano architecture. I don’t have a time frame. However, should we get access to unlocked CPU and GPU ratios, it’d become much easier to push each component of this 32 nm part as far as possible without running afoul of interfaces without as much tolerance for scaling.

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