Influence of L2 Cache on Performance
Before comparing the performance of the new AMD Sempron 2600+ to other CPUs, we wanted to check out the influence of the size of the L2 cache on the performance of the system with a K8 processor. When testing CPUs on ClawHammer and NewCastle cores earlier, we had noted that the reduction of the L2 cache from 1 megabyte to 512 kilobytes had had a very slight impact on the performance. There are several reasons for that.
First, all K8 processors have an exclusive cache. It means that data stored in the L1 cache are not duplicated in the L2 cache. Thus, the total effective capacity of the cache memory is the sum of L1 and L2 caches. Second, the L1 cache of K8 processors is rather large by itself, 128 kilobytes. Third, each K8 CPU has an integrated memory controller, which helps to reduce the memory access latencies in comparison to processors that communicate with the memory via the chipset. That抯 why the reduction of the L2 cache doesn抰 affect the performance of K8 processors as dramatically as, for example, it does with CPUs of NetBurst architecture (but to be frank, when scrutinizing the new CPUs of the Pentium 4 6xx family, we noticed that the doubling of the L2 cache brought just a minor performance gain to them).
By the way, the influence of the size of the cache may become stronger in 64-bit modes as the length of data and addresses as well as of instructions is going to grow up. So, the load on the cache memory is evidently going to be higher in 64-bit applications.
But the Semprons don抰 support 64-bit extensions and thus should be more tolerant to a reduction of the L2 cache. To check this out in practice we decided to compare several Socket 754 processors clocked at the same frequency, but equipped with different amounts of L2 cache memory. This test will tell us what risks AMD is running by having further reduced the L2 cache in its new Socket 754 processors, namely in Sempron 2600+ and Sempron 3000+ models.
For this test we took a Sempron 2600+ (128KB L2 cache), a Sempron 3100+ (256KB L2 cache), an Athlon 64 3000+ (512KB L2 cache), and an Athlon 64 3400+ (1024KB L2 cache) and set the clock rate of each processor to 1.6GHz. The CPUs were tested on the following testbed:
- DFI LANPARTY UT nF3 250Gb mainboard (Socket 754, NVIDIA nForce3 250Gb);
- 2x512MB Corsair CMX512-3200XLPRO DDR400 SDRAM (with 2-2-2-10 timings);
- PowerColor RADEON X800 XT graphics card (AGP 8x, 500MHz/500MHz);
- Western Digital Raptor WD740GD hard disk drive (Serial ATA-150).
We performed our tests in Windows XP with Service Pack 2.
