Hyperthreading, Dual core and SMP missing proper support in 4.1.6 iso

[Dekard]

After quite a bit of testing on a dual processor HP Kayak xm600 workstation with dual pIII 750's I was able to confirm that the default kernel installed by the Sage 4.1.6 iso is lacking support for Hyperthreading, Dual core and SMP systems. Note that all the systems will boot and run SageTV fine however you will be running all these systems without the benefit of hyperthreading or the second core\processor.

Let me explain further, on Hyperthreading, Dual core and SMP system you need what is called SMP support in the kernel so that the operating system (Gentoo) has access to the second processing unit in the hardware. Note that the second processing unit maybe another processor, a second core or simply a virtual one (hyperthreading).

So, lacking the ability to see the second processing unit the system will only be using one unit. You would effectively be losing half of the available processing power of a dual core or dual processor box. Hyperthreading enabled boxs would loose performance as well, but at a lower rate do to the fact they do not, in fact, have a second processor, merely a virtual one.

My tests were conducted on a HP Kayak xm600, which is a fairly standard design. I tested with a matched pair of pII 533's and a matched pair of pIII 750's. A full repartition and reinstall was completed between the swaping of the processors.

Please note: I was able to properly use Sage for months on the power of one pII 533. I had no idea the other processor was going unused in this config and frankly, it was not needed. The only issue I ran into was this problem, and thats not a problem you would ever experience running Sage in a normal environment. I had to be heavily taxing the system before I could tell I was actually not getting the power of the second processor.

What does this mean for you? Well, I've got a couple of thoughts. I'll break them into categories that seem to make sense to me at the moment.

First, normal users. You just want a linux install that works. You don't plan of recompiling the kernel or installing a gui like kde. You bought this because you wanted to use Sage on linux. You will never, never need to worry about this. Ever. You do not need the power of the second processing unit.

Second, power users. You want to use your box for more that just Sage. You know you are wasting the potential of a nice box. Folding for a cure, running a desktop os or just hacking around, you plan to do it all. Or at least some of it. How will this affect you? Well... You would be able to notice from the system monitor in KDE or your gui of choice that you are only seeing one processor. Going to the command prompt and typing top and hitting 1 would show you cpu0 and not cpu0 AND cpu1. You should be seeing two though, after all thats what you paid for. So, multitasking a lot, or using another application along with Sage will definately be slower on this system then it should be. But, you may not need all the power.

Third, super power uses. You demand the ultimate in performance. The ultimate in pvr software (thats why you bought Sage, right?) and you want cutting edge stuff. NOW! You aren't afraid to compile your own sources. You know what you want and you want it all. In this case you are being affected. You are not getting what you installed. There is unused processor cycle, man. Put them to use!

Fourth, OEM and large scale system builders. If you are building a high end box, something with 5+ tuners, a large number of clients, software raid or anything else truely demanding you will have zero benefit from building a muilt core or multi processor system. You might as well get the fastest single core processor you can and hope its enough.

Solution 1: To correct this today you have to recompile the kernel, this time including multicore support. If you don't know how to do this, I'm not going to tell you. Suffice it to say you, can really hose your box if you don't know what you are doing.

Solution 2: Sage will have to modify their iso to allow smp support. This involves a lot of complexity as they are attempting to put out standard software on a limited budget. Including smp support will at the minimum require a second kernel included in the package and the ability to determine which one to use.

Bottom line, 90 percent of people using the Sage iso will not be affected by this. The other 10 percent know who you are. If you are up to it recomplie the kernel. Or just pester Sage to do it untill they do. But ask yourself, please, do I really need this? After all a single pIII 533 could run Sage.

[Dekard]

edited above for grammar and spelling.

[_Demo_]

The problem is some drivers used to have problem when running with SMP enabled. (capture driver for example) I don't know if it is still the case with the latest versions but for stability it was best to not enable it.

_Demo_

[Dekard]

How can we find out if its going to cause driver issues if a smp kernel is used?

[_Demo_]

There is no other way than trying.

_Demo_

[Dekard]

Originally Posted by _Demo_

There is no other way than trying.

_Demo_

I'm working on that right now. I'll post back here on my results. It will probably be a week before I have anything.

[Arawak]

Dekard, you shouldn't have too much trouble recompiling the kernel with SMP support. If you like, I can help you with this over Jabber/AIM/Yahoo/MSN - on your setup it shoudln't be more than about 30 mins.

As _Demo_ pointed out, SMP adds a lot of question marks with the kind of hardware you'd use in a PVR, so I'm not surprised they didn't enable it by default.

Cheers,

Arawak

[Dekard]

Originally Posted by Arawak

Dekard, you shouldn't have too much trouble recompiling the kernel with SMP support. If you like, I can help you with this over Jabber/AIM/Yahoo/MSN - on your setup it shoudln't be more than about 30 mins.

As _Demo_ pointed out, SMP adds a lot of question marks with the kind of hardware you'd use in a PVR, so I'm not surprised they didn't enable it by default.

Cheers,

Arawak

I'll take you up on that. I'll toss you a pm now.

[Dekard]

Well, thanks to Arawak taking one of his evening to help, I've got a working SMP enabled Sage box. So far it looks good and is connecting to a 5.0.1 box now. I'll post back here with a update on how it works in a couple of days.

[Dekard]

Originally Posted by _Demo_

The problem is some drivers used to have problem when running with SMP enabled. (capture driver for example) I don't know if it is still the case with the latest versions but for stability it was best to not enable it.

_Demo_

I'm glad to say that this issue seems to have been solved. I've been running a SMP enabled kernel on my Sage box for some time now and had no issues. One very positive side effect was a much more responsive system. I've also been able to start using the box for other uses besides just Sage and I'm enjoying it immensely. If anyone needs instructions I can take the information Arawak and I worked on and put it into useable format.

[Dekard]

Even better new, the latest v5 beta version has full SMP support out of the box. Seems this issue has been solved by the excellent Sage team in the first release following this post. I can't take the credit for this, but I'm glad to see it happen.