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_RDMSR instruction loads the contents of a 64-bit model specific register (MSR) specified in the ECX register into registers EDX:EAX. The EDX register is loaded with the high-order 32 bits of the MSR and the EAX register is loaded with the low-order 32 bits. EDX:EAX = MSR[ECX] So bit 49 will be contained in EDX register. Buggy code instead of bit 49 (CombineCr0Cd) sets bit [49-32=17] (PfcStrideDis). PfcStrideDis bit disables stride prefetch generation. This leads to memory bandwidth loss. _________ Supermicro H8QGI board After applying this change i observed huge memory bandwidth increase in tests that runs on small amount of cores. But unfortunately it doesn't affect overall bandwidth results on 4P system with 48 cores. So i think that in this system leading limiting factor is AMD HT-ASSIST feature (Probe filter). But right now it is not working. System stucks in Linux boot. I have done some experiments and figured out that stuck happens when system have cores in compute unit (CU) other than CU with BSC (boot strap core). CU is two cores (primary and seconary) that shares some things (L2 cache, FPU ...) So with probe filter i can boot Linux with one (BSC) or two (BSC + secondary core in its CU) cores. And with this configuration i can see memory bandwidth on 1 core (or two cores) close to original bios. Change-Id: I5a95f5b753d600c70d3c93d36fecc687610c61cd Signed-off-by: Konstantin Aladyshev <aladyshev@nicevt.ru> Reviewed-on: http://review.coreboot.org/2588 Tested-by: build bot (Jenkins) Reviewed-by: Marc Jones <marc.jones@se-eng.com> |
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