How efficient is i7 HT?

[sphinx99]

Back when the P4 showed up with HT, it was something of a mixed bag. Some benchmarks showed that other varying multiapplication load, you could get a few percentage points performance out of it.... greater than 0% but pretty much always still in the single digits. There were downsides too. In enterprise environments for example it was well known HT caused all sorts of havoc, by causing applications to think they were in a MP environment and switch to a less efficient multiprocessing kernel that was blissfully unaware that the purported dual-core system was really more like 1.07 cores!

The same sort of tech is back with i7 - have things changed? I see some people say "oh it's really more like 6 cores, not 8" and, well, let's just say if that were true then it's a HUGE leap beyond the P4. The benchmarks out there don't paint quite so rosy picture... it seems like you get more than the P4 HT... maybe 15% for applications that are highly threaded, but just as with the P4 there are times where HT actually holds back performance.

Just wondering if anyone has found HT to be noticeable boon or not.

 

[PAo_ReVoLT]

i would like to know that too

 

[moshpit]

I got my first real taste of HT in action just last week. This is a best case scenario, but one that I'll be CERTAINLY doing more of now that I've discovered the delight of doing so.

To attempt to make a very long story as short as possible, a bunch of us up at work had our business cell phones upgraded recently. I brought my new Blackberry home with me with all the disks and stuff I needed to go through and familiarize myself with. I was already looking very forward to the fact that this new cell has a much better ability to play movies and such that I can store on my 1Gb microsd card. My first attempt at just copying a file over and playing it was a fail. Not epic fail, just fail. A quick google provided the answer.

Loading up the Blackberry Desktop Manager, I opened the Media Manager section. I then used it to browse to a movie I wanted to convert and let er rip. I had picked a full 2 hour, decent quality Xvid movie that weighed in around a full Gb in size. I'm not BS'ing in ANY way, but the transcoding of the movie was blisteringly fast, with all 8 "CPUs" being monitored in Windows Task Manger Performance tab and Everest showing 100%, it took just under 6 minutes to crunch the whole thing down to just 450mb and kept quality totally intact for the lower resolution. I didn't even have time to finish my cigarette before it was finished.

For reference, the equally clocked Q6600, also running at 3.6Ghz, can do the same task in just over 10 minutes.

So this is a best case scenario for HT on i7. Undoubtedly, there are also situations where having HT on degrades performance by a very small amount. But it's much less often then HT on Netburst was. Pentium 4 was already a hyper inefficient architecture, HT was a bandaid for it. Now that HT isn't having to act as a bandaid, it does better overall.

Stability with HT on is totally unaffected for me, tested up to 3.8Ghz before temps made me back off.

 

[sdadept]

dont know if you remember single core/cpu machines, but the difference between them and machines with HT were massive when it comes to the desktop. HT was never meant to make your machine 2x faster. It was meant to make your machine much more RESPONSIVE. I remember having a single core/cpu amd that was more powerful than my ht intel. But the intel was better to use because I would never get the desktop minifreezes when an app hit the cpu fully.

 

[GenTarkin]

HT definitely helps if you are running any sort of folding or distrobuted computing apps that can do all 8 cores. Ive seen a 30% increase in points on WCG cunching and thats a significant amount. As to what else HT does for ya, well unfortunately it does increase temps by up to 15C in some cases vs only using 4 threads. It also is known to slow down games a bit. If you are ok with those 2 then leave it on.

Turning it off also helps OC'n the i7 if you are into that =)

 

[xorbe]

Yeah I've been messing around with HT on and off. It just depends. Some things are a win, and some are not. When you enable HT, some of the CPU's hardware resources are statically split.

With HT, you'll have better concurrency, but sometimes at the expensive of total throughput. But sometimes it's a flat-out win with HT on.

And sometimes, Windows Vista stupidly throws 2 intensive tasks onto the same core, but different threads, which can suck compared to each running on a different core.

I wrote a program in Linux, which actually runs FASTER when you run two instances on the same core (HT on), even though they don't share any data. Sounds impossible, but I have the code and output to prove it. ie, one instance takes 1 minute. If I run two copies on two cores, again 1 minute. But if I run two copies on the same core, then both finish in 54 seconds.

As you can see, it's not really predictable.

 

[sdlvx]

I've seen huge improvements with encoding video with HT on.

However, I've seen some programs totally fail with HT on. I turned it off for second life and my frame rate doubled.

I have it disabled, I get much better clocks with it disabled and I think that the smaller but constant increase in clocks is better than the hit or miss improvement with HT. Better off with it off for normal desktop usage, unless you're crunching or encoding. Probably a pretty good idea to roll the clocks down a little and turn on HT when you're encoding and then turn it off and bump the clocks up again when you're done.

 

[ÆonTrinity]

HT was good on a single core, I remember on single core's that the whole computer would freeze if you were trying to format a floppy disk but HT took care of that and other annoying freezes. Seems pointless on a quad-core to me!