Measuring bandwidth across PCI Bus

[X-Caliber]

Hi,

Is there a gauge, or some other piece of software that monitors how much data is passing through the PCI bus at any given time? My impression is that I am saturating the bus, since I happen to be a multi-tasking freak, but I would like some way to quantify this. One additional question, there are some motherboards which have USB2 ports built-in (or firewire). As data is passing through these ports, is it also passing through the PCI bus, or is there an alternate way for this data to interact with the CPU, maybe there is another bus. Before you start laughing, and remark that this is a stupid question (alternate bus!), I was merely asking because some of the newer motherboards have a gigabit ethernet controller, which I believe goes around the PCI bus.

Thanks,

-V-

[Marshmallowman]

A lot of current/new generation stuff has the integrated stuff comunicating straight through the chipset and bypassing the PCI bus altogether, that usualy includes onboard IDE,usb,network and sometimes even RAID and firewire.

And proper PCI anaysis tools are very expensive(hardware), and I don't know of any software tools for doing the job, but adding up the probably bandwidth used by your device might give you some kind of indication whats happening.

[Wombat]

Originally posted by Marshmallowman
A lot of current/new generation stuff has the integrated stuff comunicating straight through the chipset and bypassing the PCI bus altogether, that usualy includes onboard IDE,usb,network and sometimes even RAID and firewire.

Hey M, could you back that up? I know how the gig-E cards are doing it, but I'm not familiar with what chipsets feature all these other peripherals on their own bus.

[Kruzin]

Moved to General Hardware/Software

[rugger]

Originally posted by Wombat
Hey M, could you back that up? I know how the gig-E cards are doing it, but I'm not familiar with what chipsets feature all these other peripherals on their own bus.

All newish chipsets don't use the PCI bus for their internal functions anymore.

Old chipsets had a northbridge, which has a PCI, memory and AGP buses on it. The southbridge contained all the other built in functions, and was connected to the rest of the computer using the PCI bus. Hence, we had wierd chipsets like the AMD640 northbridge with a VIA 686B southbridge

Newer chips have a northbridge with the memory and AGP controllers on it, and a speciallised bus controller which runs much faster then PCI. The southbridge is then connected to this bus, and all its onboard functions are accessed via that specialised bus rather then the PCI bus. The southbridge also contains the PCI controller now instead of the northbridge, since I guess that chipset designers now consider the PCI bus to be too slow to put into the northbridge. View some of anandtech's reviews of the Intel 820 chipset, and the nforce, and via KT266 chipsets to get more info.

[Marshmallowman]

Like rugger said they are all doing it...but here is a specific one sis 748

note: the integrated stuff is not connected through the PCI bus, but directly to the chipset and through the mutol

http://www.sis.com/products/chipsets/oa/socketa/748.htm

and intel 875 has something similar, where the devices and pci slots have separate connections to the chipset.

http://intel.com/design/chipsets/875P/index.htm?iid=ipp_desk_chip+prod_875p&

[X-Caliber]

I see, so then having USB2 ports built directly into the motherboard would be a much better idea then buying a PCI card with USB2 ports, since the PCI bus has a (theoretical) 133M/s limit. But then why don't manufacturers build the SCSI controllers directly onto the motherboards too (and attach it to the specialized bus controller), rather then sucking up all the bandwidth of the PCI bus. And for that matter, wouldn't it make more sense to make all adapter cards (say HDTV tuner cards, or other data intensive devices) USB2 based, since they don't have to make use of the PCI bus? Thank you for the replies, and sorry Kruzin for the double post, and for posting in the wrong forum!

[Marshmallowman]

Yup, except some integrated components are actually normal chips connected through the PCI bus.

The key thing is integrated chipset devices as integrated motherboard device may mean it is actually a normal PCI device.

I think almost all new mobo's have full integrated chipset USB 2. A year ago a lot of them were add on chips.connected through the PCI bus.

[rugger]

Originally posted by X-Caliber
I see, so then having USB2 ports built directly into the motherboard would be a much better idea then buying a PCI card with USB2 ports, since the PCI bus has a (theoretical) 133M/s limit. But then why don't manufacturers build the SCSI controllers directly onto the motherboards too (and attach it to the specialized bus controller), rather then sucking up all the bandwidth of the PCI bus. And for that matter, wouldn't it make more sense to make all adapter cards (say HDTV tuner cards, or other data intensive devices) USB2 based, since they don't have to make use of the PCI bus? Thank you for the replies, and sorry Kruzin for the double post, and for posting in the wrong forum!

Unfortunately, I don't think most of the north/south bridge links are multipoint, so they can't really handle multiple devices, like extra scsi controllers and such. Also, thats what PCI-66 and server motherboards are for ... high bandwidth SCSI.

Also, I am not convinced about the argument to put devices onto the USB2 instead of the PCI bus. While the USB2 bus does have a potentially less congested path to the CPU, the operation of the USB2 bus is certainly not as cheap as the PCI bus in CPU cycles. Thus, most high bandwidth devices, like ethernet adapters and hard drive controllers should be put onto the PCI bus. Firewire might be somewhat better, but I am still skeptical any external bus would really match the overall performance of the PCI bus.

However, saying that, there are TV encoders, hard drive controllers and CD burners, and sound cards like the sb exidiligy (or so stupid name I can't spell) for the USB bus, so it isn't an utterly terrible way to expand your system with high bandwidth devices. With USB also being portable and basicly plug and play, these can easily outwieght the CPU cost.

[Kurt]

FW800 is probably very close to the PCI 32/33 speed. Too bad it's not more common.

[X-Caliber]

"FW800 is probably very close to the PCI 32/33"

its too bad that FW800 isn't integrated into the current Intel 875P chipset. I think it has a lot to do with the royalities Apple would get from Firewire. If it weren't for that, people would never even use USB.

From this:

http://intel.com/design/chipsets/875P/pix/875_schematic.gif

I just assumed that the integrated components were all independent of the PCI bus.

[dZeus]

Yup, and that's exactly why Intel has some of the fastest performing PATA/SATA RAID0 implementations on their ICH5R southbridge.

Too bad that raid0 is kind of useless for normal desktop use (only stuff like video editing takes advantage of the higher STR).

[Kurt]

Another reason why Intel has no interest in implementing FW is that it doesn't require (much) CPU power -contrary to USB that's much more CPU dependent.

Since USB is now a piece of cake for Intel P4, they offered us USB 2.0 (a boon compared to 1.1 in transfer speed) and software RAID in the form of ICH5R (sorry, I forgot AC'97 sound).

Their CPUs are so damn fast they're not required for office work - so they need to invent more "stuff" that uses them...

I wonder what they'll find next...

[dZeus]

Software raid has been around for ages. It's not a selling point for CPUs, it's something board manufacturers request motherboard chipset vendors, because otherwise they'll need 3rd party chipsets which increase costs more than an integrated solution. Same for AC97 sound.

USB2 is more cpu dependant, in order to shave down costs to implement it (both on devices as on controllers). Unfortunately that exact reason seem to cause FW to lose terrain to USB2 on lots of fronts (I rather have a non-cpu hogging bus to attach pheripheals).

[Kurt]

Yes, but software raid was a small part of the MB market, as was AC'97.

Now AC'97 is virtually on all MB's. Soft RAID is next.