In a related question (http://superuser.com/questions/412988/impact-of-the-l3-cache-on-performance-worth-a-dual-processor-system) I asked about the benefit of a dual-CPU system in terms of doubling the L3 cache.
However, I have noticed that the Xeon E5-2600 series of CPU's has exactly 2.5 MB of L3 cache per core (http://en.wikipedia.org/wiki/List_of_Intel_Xeon_microprocessors#.22Sandy_Bridge-EP.22_.2832_nm.29).
This leads me to believe that the operating system reserves 2.5 MB of L3 cache per core. However, I also have the contradictory impression that the L3 cache is shared among all cores. There is surprisingly little information or discussion about this.
My major concern is whether low-priority background applications might "hog" the L3 cache and slow down performance for higher-priority foreground applications. Two specific performance problems that I have motivate this question.
(1) Compiling a certain C++ program requires 25 minutes on my current development system in VS 2008, whereas on another system it goes vastly faster, requiring only 5 minutes on VS 2008 with identical settings - despite the fact that I have a near high-end i7-970 CPU and sufficient RAM.
(2) Programs often take up to 20 seconds to run (i.e., display their main window) on my system; and on a related noted, the Windows shell requires up to 10 seconds to display the Windows Explorer context menu (and related behaviors also take about as long), despite my attempts to limit the context menu entries (there are currently perhaps 10 additional ones beyond the default).
My system is certainly loaded with a very large number of applications that I have installed (and uninstalled) over the years, but I do my best to streamline the system nonetheless.
I also have many low-priority background applications running; in particular redundant cloud backup software such as CrashPlan, which typically add up to utilize about 25% of the total CPU utilization on this 6-core 12-thread system.
I will be getting a new computer. I know that I will continue to be running many background applications, and installing/uninstalling many programs. If I thought that getting a dual-CPU system that doubles not only the cores but the L3 cache would assist with overcoming the horrible C++ compiler performance and the general system slow-down, I would gladly do it.
There should be no reason why a high-end system operates so slowly, even with many programs and background applications. But if my problems will occur no matter how much CPU power and L3 cache I give the system, simply because I do have so many programs and background applications installed and running, I don't want to waste $2,500 additional dollars on a dual-CPU system that won't help solve my problem.
Any suggestions, in particular regarding my question about whether the L3 cache is shared among all cores (such that low-priority background applications might conceivably be hogging the L3 cache, slowing down higher-priority programs), or rather if it is tied to individual cores, would be appreciated.