Performance: ACPI vs. NON-ACPI on Laptops

Hey guys!!!
I have an issue and I can’t find answers on the web. Before asking, let me put a few concepts:
• ACPI stands for Advances Configuration and Power Interface. When enabled, Windows will have all the power Management like hibernation/ Power Off without “physical button”, etc. Also, I will also AUTOMATICALLY ASSIGN IRQs to devices.
• You will see a LOOOT of IRQs (run Msinfo32.exe, Hardware Resources->IRQs). It is important to POINT that the computer ONLY HAS 16 PHYSICAL IRQs. The others are virtual IRQs created by ACPI.
• Sharing IRQs with different devices IS POSSIBLE.

It is well known that having a single device per IRQ is VITAL if you need PERFORMANCE! This is because the CPU will attend just one device at a time when “listening” to that specific IRQ. It applies in my case, since I do Music Recording, and I need real-time processing (Very Low Latency). If the audio card is sharing IRQ, we get clicks and pops.
Up to now, all “PC musician” have solved this by installing Win Xp as STANDARD PC, which let you manually assign IRQs to PCI slots in the BIOS.
Now…I just have my new HP dv9500t Pavillion Laptop. As many, the BIOS is tiny and doesn’t let me change ANYTHING. The question: What is the best HAL for a new laptop?

• Standard PC DOESN’T WORK, since it doesn’t support DUAL PROCESSOR (core 2 duo in my case)
• ACPI Multiprocessor PC. It will work. However, it will manage my IRQs, and I may want to do it ‘as in the past days’, to gain performance. However my BIOS doesn’t let me do that. Any ideas?
• MPS Multiprocessor PC. Microsoft says “Applies to non-ACPI computers with a dual processor running.” Will this apply to a modern Laptop? How?

Does a Laptops really NEED Power mngement? Why ACPI does both power mngement and IRQ sharing? Any way to keep the Nice POWER Options but handle IRQs differently? I’m sure MANY USERS would need ULTRA PERFORMANCE PCs: Video editors, musicians, Servers, 3d designers. Once again. Sharing IS possible. I just don’t want it. Also, ACPI is a little “STUPID”, since it will assign many devices to the same IRQ, still where there are a few 100% free IRQs.

Any idea, question or comment will be really appreciated!
Thank you very very much!

Danny Bullo

 

No, it is well known that this applied back in, oh... the Win95 days.

You might find this worth reading:
http://support.microsoft.com/kb/314068

Anyway, there really isn't much to do. If ACPI is enabled, it will manage IRQ's for you. And the reason it does this (as the above article says) is because this stuff is getting pretty damn complex. It's not like in the old days when you had the sound card on IRQ7 and... maybe one or two other IRQ's in use.

(On the upside, it's not as big a deal as it used to be. You won't get IRQ conflicts, and performance isn't really affected either). ACPI is designed to solve these problems.

If you disable ACPI, you're basically back to the Pentium 3 days (if not earlier). Which means a lot of things will probably stop working properly (and you'll be able to get IRQ conflicts again)

IRQ's are kinda meaningless these days. They still exist, yes, but how they work, and how they're controlled is very different from how it worked "back then". Don't automatically assume that 15 years old wisdom about them still holds.

 

Thanks a lot Jalf!!!
Actually, it makes sense. I'm not saying the actual system is not good. As you said, it IS good, since it can live with the devices getting more and more damn complex. However, it closes the doors to users as musicians, video editors, etc. how want to TAKE FULL ADVANTAGE of their hardware, for realtime purposes.
You will be surprised to found in musicians/ audio producers forums, how many people have $5555555 computers and still claim that they cant work on low latency or they get clicks and pops after recording 5 audio tracks!!!
MAny solve that by just having non acpi systems, changing PCI slots until they see that , at least, the audio card, doesnt share IRQ al all!!!
Thanxks anyway for your input!!

ps: Actually, i wanted to know what you thiunk about that. In my case, I will install xp under "ACPI Multiprocessor PC", since my bios doesnt let me do anything, it that right? or shouls i install under regular "ACPI COMPUTER"?

Danny Bullo

 

Well, how much of this is just old "superstition"? (It used to be true, so we keep following these rules of thumb, without checking whether it's still necessary)

I don't know enough about the requirements of audio producers to give you a precise answer, but I'd imagine that as the overall speed of computers has increased, latency has become less of an issue.
But as I said, I don't have any first-hand experience in this area, so I could be wrong.

I'm not sure, tbh. I've never been able to find a detailed description of what each one means. (Does dualcore CPU's count as multiprocessor? Or is that only for multi-socket systems with multiple physical processors?)
But yeah, I'd probably go with the ACPI Multiprocessor one too.

 

There was a trick I used to do on desktop machines when wanted my brother's professional sound cards to work on particular IRQ since he was bothering me with questions like this thread covers. I would block particular IRQs in BIOS and then start windows. Devices would "move" to the free IRQs, then I would add his card and free one particular IRQ. It would usually use only that IRQ and stay there alone. That way I was having ACPI and some devices using only one IRQ at the same time. He is using XP and says that it works now as it should.

Now Notebooks cannot do that (well none of mine at least - BIOS is poor). And I think that today new sound cards are working well with ACPI. I also use Vista and wonder if the same trick applies there too. Probably does.

Ivan

 

The problem is that Windows is not a "real-time" operating system. It doesn't guarantee a response within a certain amount of time to different interrupts, which is why you see the expensive computers still including those pops and clicks.

Many people have started looking into systems like Medibuntu, which is a full operating system tuned to having real-time response in sound cards and the like, where hardware access is prioritized over everything, essentially. If you are in the USA, there may be legal issues with you distributing or using certain extended parts of Mediubuntu like DVD decoding and so on, but for the sake of the discussion I'll assume you aren't. The base system should be perfectly acceptable and legal, including all the audio software and drivers, because they don't go around any kind of DRM restrictions. Don't take my advice though, I'm not a lawyer.

For your case, with Windows, use the ACPI Multiprocessor PC driver. That's the driver that is best tuned to your system. The BIOS doesn't expect you to be able to manually set your IRQ's and such.

That said, you may try experimenting with the MPS Multiprocessor Driver. If your machine boots, that's the only multi-CPU driver that is not ACPI-aware, and thus may do what you want it to do. But that's not saying what you want it to do makes sense to do

 

ikovac and PitaBread:

Thanks mates!!!!!
That is right.....Windows is not a realtime OS. I've been in this field and read a lot about it! However, a well tunes machine could work PERFECT for realtime apps, like audio and video. I.E: I have a Pentium IV at home with a professional audio card. It it set to STANDARD PC, and I got rid of all pops and click, even at the lowest latency!!!! That was at the expense of not using HyperThreading, since Standard Pc doest recognizes HT (like a second processor). I think I will install with ACPI Multiprocessor PC driver. Since the BIOS doens tlet me do ANYTHING, it makes no sense to do with MPS Multiprocessor Driver. I think MicroSoft keeps "inventing " windows and they keep reusing the old written code and thus.....OSs sucks.... Vista could have been a GREAT step forward.....however, it sucks...It is a resource hog.....just for a not so great User interface!!! Im gonna wrtite a new post about this:
Vista vs Xp DCP:
In vista, is useless.....for some reason DPC times is high.. Back to XP with the same machine, it very very low!

Thank you very much!

Bullo