virtualbox.org

Hi! I asked here about CPU wich would give opportunity to maintain 5-7 Windows guests at once and found that as much more cores it has it's better.

So I bought AMD FX-8120 with 8 cores and it was "fail" It's ok to start Win XP guest but there is a big problem with Win 7 guest

I have 2 host PCs - 1st with i5-2500k and another one with FX-8120, both machines with Win7 64 Host. On the first I started 7 Win7 guests and everything was ok. But on second - only 5 XP guests and 1 Win7. Every Win7 had the same configuration (1Gb of Ram), but on i5 no problems and on fx - lags, freezes etc. I tried to increase amount of cores for guest, tried to give more RAM, nothing helped for fx

May be there are some secrets of win7 guest configuration on AMD proccessor? Or it's really piece of sh*t?

PS it's not advertisement or black PR, I just want to find the reason why there is such difference?

There are many aspects to CPU performance, and the kind of application you are trying to run is of supreme importance.

For example, if the application is heavily I/O laden (I/O bound) then the CPU performance is essentially irrelevant: FSB speed, memory and network speed (depending on the type of I/O ) are all more important. Ditto for graphically bound apps, which will run especially badly inside a VM. Note that even if you have an 8 core CPU you only have one bus (one shared path to external memory), so if your apps are I/O bound they will all be falling over each other. Win7 is certainly an I/O hog as it starts up, multiply that by a large factor if you have antivirus installed.

It doesn't apply to your scenario, but if you assign multiple cores to a VM which is only running one single tasking app then the extra cores are just a dead weight.

Basically to get best performance you have to use knowledge and judgement, there is no magic formula.

mpack wrote:There are many aspects to CPU performance, and the kind of application you are trying to run is of supreme importance.

For example, if the application is heavily I/O laden (I/O bound) then the CPU performance is essentially irrelevant: FSB speed, memory and network speed (depending on the type of I/O ) are all more important. Ditto for graphically bound apps, which will run especially badly inside a VM. Note that even if you have an 8 core CPU you only have one bus (one shared path to external memory), so if your apps are I/O bound they will all be falling over each other. Win7 is certainly an I/O hog as it starts up, multiply that by a large factor if you have antivirus installed.

It doesn't apply to your scenario, but if you assign multiple cores to a VM which is only running one single tasking app then the extra cores are just a dead weight.

Basically to get best performance you have to use knowledge and judgement, there is no magic formula.

The task for every guest is a simple order of operations - open web, copy info, calculate, save in excel. But on i5 it works much faster with win7. Both host are really similar - RAM, HDD, etc. The differences are CPU and motherboard. So I think that intel architecture is more suitable for multi guest process. But speaking the truth I forgot that FX uses internal video memory and i5 mounted with external video card. May be there is bottle neck?

And can you estimate if I use SSD insted of HDD - it will really help? And what is the best way - install virtualbox on SSD with virtual hdd files or it will be ok to have these files on ordinary HDD?

Johnyman wrote:But speaking the truth I forgot that FX uses internal video memory and i5 mounted with external video card. May be there is bottle neck?

Graphics performance tends only to matter much with video games, HD video etc. However for best performance, yes the external video card will perform better since things like display refresh will not require PC SDRAM accesses, leaving lots more RAM bandwidth available for the app.

A good SSD has a fast turnaround, so would make one app go faster. But, I wouldn't really expect it to make a huge difference to overall system performance: if many tasks are running and DMA is being used for I/O then time spent waiting for I/O DMA to complete will be spent executing other things. Let's put it this way - an SSD shouldn't make things worse, unless you start running out of disk space!

mpack wrote:

Johnyman wrote:But speaking the truth I forgot that FX uses internal video memory and i5 mounted with external video card. May be there is bottle neck?

Graphics performance tends only to matter much with video games, HD video etc. However for best performance, yes the external video card will perform better since things like display refresh will not require PC SDRAM accesses, leaving lots more RAM bandwidth available for the app.

A good SSD has a fast turnaround, so would make one app go faster. But, I wouldn't really expect it to make a huge difference to overall system performance: if many tasks are running and DMA is being used for I/O then time spent waiting for I/O DMA to complete will be spent executing other things. Let's put it this way - an SSD shouldn't make things worse, unless you start running out of disk space!

One more thing I cant understand. I see that guest CPU is 100% loaded, but host CPU cores work at 50-60% maximum. So host CPU is available but guest cant use it fully and it's also connected with DMA I/O?