Hi Richard, I am having some trouble understanding the implementation of MTRR handling in Linux. I am trying to see the performance impact by disabling all cache. As a first step I am disabling MTRR. Intially when I boot up my mtrr file is as following: $ cat /proc/mtrr reg00: base=0x00000000 ( 0MB), size=131072MB: write-back, count=1 reg01: base=0xcff00000 (3327MB), size= 1MB: uncachable, count=1 reg02: base=0xd0000000 (3328MB), size= 256MB: uncachable, count=1 reg03: base=0xe0000000 (3584MB), size= 512MB: uncachable, count=1 reg04: base=0x1ff0000000 (130816MB), size= 256MB: uncachable, count=1 There seems to be a discrepancy because I have 8 gb RAM in my system. Now I run an OmpSCR benchmark ------------------------- $ ./c_lu 800 This program is part of the OpenMP Source Code Repository (OmpSCR) Program: ./c_lu Description: LU reduction of a dense matrix. Argument size 800 Argument NUMTHREADS 1 Running ... Timer EXE_TIME 1.645332 ----------------------- So, I go ahead and disable the write-back cache as follows: $ echo "disable=00" > /proc/mtrr $ echo "base=0x00000000 size=0x80000000 type=uncachable" > /proc/mtrr Now I again run the benchmark $ ./c_lu 800 This program is part of the OpenMP Source Code Repository (OmpSCR) Program: ./c_lu Description: LU reduction of a dense matrix. Argument size 800 Argument NUMTHREADS 1 Running ... runs for a verry long time.(> 10 min) So there is some effect of disabling MTRR. Again when I enable the MTRR, I am not able to restore to intial state. $ echo "disable=00" > /proc/mtrr $ echo "base=0x00000000 size=0x80000000 type=write-back" > /proc/mtrr Even after doing this, there is no speedup compared to disabling MTRR. It will really be helpful if you could point me as to where I am wrong. Thanks, Andev. -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
