Thursday, July 14, 2011

Sandy Bridge - more on Performance in Second Life

Hi everyone, 

I've found that Lenovo has a very nice feature in their Power Manager thingie that shows you the percentage of Turbo Boost (over-clocking) that you're getting on your processor(s) and the on-chip graphics unit.  My laptop has Intel's i5-2410M, so has a nominal processor frequency of 2.3 ghz and a max of 2.9 ghz.  Its on-chip graphics unit, the HD 3000, has a nominal fequency of 650 mhz and a max of 1.2 ghz.  You can get the full specs here if you're interested:

As a reference point, when doing little to nothing (like now, while I'm typing this) the processor is usually idling at 34% of its nominal frequency, and the graphics is listed at 100%.  Yep, the latter seems odd to me too - but there you have it.  That value of 34% works out to a frequency of 2.3 * 0.34 = 0.782 ghz.  As a check CPU-Z reports that the cpu is at 798 mhz, or 34.08%... close enough!

So... how does this all work in SL?  Just wandering around in a sim, I usually see the processor clocked at 117% or 2.7 ghz.  In some sims, perhaps even most, its hard to be sure, the frequency of the graphics remains at a nearly constant at 100%.  I do see it blip up now and then but that's not the norm for most places.  Yet in other sims, as I walk around I see the frequency of the graphics controller go up substantially, usually to somewhere around 1 ghz, about 150% of its nominal value.  It will vary around that value, but calling it 150% of nominal is a fair average.  Also in some places if I light on a pose-ball and zoom in, the graphics frequency will go even higher up to 184% and stay there.  That works out to the maximum clock frequency for the Graphics unit of 1.2 ghz.  I haven't been able to determine why this is happening, but it's not random at all, its quite repeatable.

So that's Turbo Boost.  It seems to be working nicely in SL.  In effect I have a faster processor and graphics unit than the one I bought when needed.

But... how about the number of processors?  How many are useful in Second Life?

My conclusion on the number of processors is mixed.  First, it's pretty clear that the SL viewer code does very little to make use of multiple processors if you're just wandering around in one sim.  I see this as I look at the task manager in windows.  Since Windows treats my laptop's 2 hyper-threading processors as if they were four normal processors, it shows a utilization of about 24% to 27%.  One processor/thread's worth of work.  Its a shame, there's a lot of processing power sitting idle.

There is good news though.  When you tp from one sim to another, the viewer issues a bunch of requests for textures.  If you have a fast connection to the network, they can arrive in a burst, pouring in pretty quickly.  During this time, I've seen the utilization go up substantially and approach using all four processor threads fairly heavily.  If I turn off hyper-threading, effectively reducing the 'number' of processors that windows sees to 2, I can 'feel' the difference when tping.  It takes longer for things to rez.  And I can see the processor utilization of the two remaining processors 'peg' indicating that more power would be useful. 

So for processors, Yes, Sandy Bridge's two hyper-threading processors are useful for SL.  But only when tp-ing between sims AND you have a high speed connection to the internet. I don't have a system with 4 hyper-threading processors (the i7) to try SL out on, but since my 2 hyper-threading processors are not 'pegging', I would not expect any additional improvement.

One thing to remember is that this is all done with a laptop (Lenovo Edge E420s).  Laptops have very limited cooling capabilities and processor chips are designed and managed with that in mind.  A desktop system with an i5 sandy bridge will have better cooling capabilities and I would expect Intel to take advantage of that and achieve even more performance.


[edit -- oops, I mean to add links to two previous posts relating to sandy bridge and amd's competing fusion.  I'll sneak them in now! ]

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