It's Really Not Qualcomm's Fault

We've established that webOS has been and could be ported to different SoCs from different vendors – there's nothing tying it irrevocably to Qualcomm. The next is a discussion of the performance delta that existed because of differing hardware between tablet vendors. The Next Web wrote a story today claiming that webOS could run over 2x as fast on an iPad 2 than on an HP TouchPad. The claim gets even more interesting:

"With a focus on web technologies, webOS could be deployed in the iPad’s Mobile Safari browser as a web-app; this produced similar results, with it running many times faster in the browser than it did on the TouchPad."

I'm going to ignore the whole "because it's webOS it can run in a web browser" argument but let's get to the performance discussion. While webOS and Mojo do make substantial use of JavaScript, CSS, and HTML5, that doesn't necessarily mean the entire OS itself can be a web application. Don't forget the Palm PDK as well, which runs much closer to metal than the Mojo SDK.

Anyhow, the TouchPad uses Qualcomm's Snapdragon S3 APQ8060. It has two Scorpion cores running at 1.2GHz, a shared 512KB L2 cache and a dual-channel memory controller. In the TouchPad there's only a single 1GB DRAM on board. It's unclear if there are two DRAM die on that package or not, so whether or not the SoC is actually given full access to 2 x 32-bit LPDDR2 devices is unclear. The CPU cores are in-order and feature a pipelined FPU and NEON unit. On the GPU side the APQ8060 uses Qualcomm's Adreno 220.

If this hardware sounds familiar to you it's because it's the modem-less version of the MSM8x60, the same SoC used in the HTC Sensation and the EVO 3D.

The iPad 2 uses Apple's A5 SoC manufactured by Samsung. It has two ARM Cortex A9 cores, a 1MB shared L2 cache and a dual-channel memory controller. The A5 in the iPad 2 comes in a PoP (Package-on-Package) configuration with the DRAM stacked on the SoC die. Although it's physically unclear whether both channels are populated, the Samsung DRAM part number on the A5 indicates a PoP stack with two DRAM devices. In other words, the A5 is running in dual-channel mode. The CPU cores are out-of-order, feature a pipelined FPU and NEON unit. Imagination Technologies supplies the PowerVR SGX 543MP2 GPU in the A5.

From a CPU standpoint, Apple has a performance advantage at the same clock speed, but Qualcomm runs its cores at a higher clock. NVIDIA claimed that the move to an out-of-order architecture in the A9 was good for a 20% increase in IPC. Qualcomm has a 20% clock speed advantage. In most situations I think it's safe to say that the A5 and the APQ8060 have equally performing CPUs.

Apple does potentially have a memory bandwidth advantage as it's unclear the memory configuration of the TouchPad. I did wonder if this might be a reason why UI transitions were so slow on the TouchPad. In order to deliver a smooth UI you need good GPU acceleration built into your OS and you need sufficient memory bandwidth for the screen. At 1024 x 768 you need 180MB/s of memory bandwidth to render a UI at 60 fps. That's assuming no overdraw or multi-pass blending effects. With only a single LPDDR2-667 channel there's only 2.7GB/s of theoretical memory bandwidth. In practice you generally get 80% of peak theoretical memory bandwidth, that takes us down to 2.1GB/s. If we assume webOS was really inefficient in drawing its UI and needed 7x the bandwidth per frame, that still leaves us with 840MB/s of bandwidth available for the rest of the SoC. Assuming the CPU cores aren't doing anything, that's enough to provide a smooth, 60 fps UI. Start taxing those CPU cores and their bandwidth demands could go up to a few hundred MB/s, perhaps even more. Let's not even mention what happens if the GPU starts cranking away.

Now if we assume that webOS is super efficient, then even a single LPDDR2 channel is more than enough to deliver a high speed UI. In my calculations above I assumed a 7x increase in memory bandwidth requirements per frame. If we knock that down to 4x we nearly double the amount of memory bandwidth available to the rest of the SoC.

My point here is that the Qualcomm hardware is technically fast enough to deliver a smooth UI in webOS. The problem wasn't the hardware.

As far as CPU performance goes, here's a graph comparing the Tegra 2 based Galaxy Tab 10.1 to the A5 based iPad 2 in Sunspider 0.9:

SunSpider Javascript Benchmark 0.9

Granted this test measures the entire hardware and software stack (browser, OS) and does show a ~2x performance delta between the TouchPad and iPad 2, but it shows that it's physically possible to build a tablet that has performance similar to the iPad 2. Furthermore, we've already shown that NVIDIA's Tegra 2 performs similarly to Qualcomm's dual-core SoC in other situations. Completing the circle it's safe to assume that at least from a CPU standpoint, Qualcomm's APQ8060 wasn't the factor holding back the TouchPad, it was software.

The only area where the iPad 2 could conceivably be 2x the speed of the TouchPad due to SoC hardware alone is in GPU performance. However the claims above say the performance advantage was demonstrated in a browser window and not in a cross-platform OpenGL ES 2.0 game.

These days Qualcomm's high end dual-core SoC is comparable to TI's and NVIDIA's. Each platform has its advantages but I find it very difficult to believe that Qualcomm was somehow responsible for the poor performance of the TouchPad. 

It's Not Qualcomm's Fault webOS Needed Work
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  • kmmatney - Saturday, August 20, 2011 - link

    Damn....that's cheap! Reply
  • piiman - Saturday, August 20, 2011 - link

    they are sold out now :-( Reply
  • Stuka87 - Friday, August 19, 2011 - link

    Arstechnica had an article today about this exact subject, and about how the hardware was such a limiting factor, and how it was designed over a year ago, and a bunch of other stuff.

    And I was really quite sure that this could not be the case (in reference to speed). So thanks for taking the time to clear things up Anand.

    I am bummed that WebOS may go the way of the dodo, as I really liked the interface and the way it acted. But it is slow, even on the TouchPad which has a lot of hardware.
    Reply
  • killerroach - Sunday, August 21, 2011 - link

    That being said, Ars does have a pretty long-standing tradition of taking glee in the hardships of anybody not named Apple. Reply
  • AmdInside - Friday, August 19, 2011 - link

    What about developer relations? It is a key that many big companies use to push their products by offering development assistance to help the customer make a better product. Look at how well tuned apps are to intel processors because of this. Perhaps Qualcomm did not provide sufficient assistance to HP to make WebOS as fast as it could be.

    I picked up a couple of Touchpads this evening. Fingers crossed that someone can figure out a way eventually to get honeycomb on the Touchpad.
    Reply
  • DanNeely - Friday, August 19, 2011 - link

    I don't know if they actively sought developers out; but it appears they were responsive to anyone who contacted them. A friend of mine contacted HP and offered to port one of his employers games if they gave him hardware. He got both a phone and a tablet to play with. Reply
  • GrizzledYoungMan - Saturday, August 20, 2011 - link

    How poopy the actual Android user experience is. Reply
  • kmmatney - Saturday, August 20, 2011 - link

    Have to agree...I tried an Android tablet, but the user experience just wasn't there, so sold it and paid a lot more money for an iPad2. I'm itchin to upgrade my 2+ year old 3GS, but at the moment Android is a downgrade, so I'm just waiting for the next iPhone. I'll probably have to wait a month or more after it comes out because of all the hoopla. Pain in the ass to be tied to Apple products, but the user experience is worth it, IMO. Reply
  • piiman - Saturday, August 20, 2011 - link

    Please define "user experience" Reply
  • Sterman - Saturday, August 20, 2011 - link

    you know... that magical thingy that makes you feel good inside. Reply

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