Description of problem: The aic7xxx and aic79xx drivers have high memory IO disabled (the can_dma_32/single_sg_ok flags are unset in the SCSI driver template structure). This is because the driver sources check for the CONFIG_HIGHIO macro which, in the AS2.1 kernels, is persent in the kernel .config, but not set in include/linux/autoconf.h. This will lead to performance losses in systems wirth large memory. Version-Release number of selected component (if applicable): 2.4.9-e.xy up to 2.4.9-e.38 How reproducible: always Steps to Reproduce: 1.Install RHAS2.1 on system with aic7xxx or aic79xx controller and >1GB memory. 2. Use "new" driver (aic7xxx 6.x.y) for aix7xxx. 3. Do I/O. Actual results: System uses bounce buffers. Expected results: System doesn't need bounce buffers. Additional info: I came a cross this problem accidentally by comparing the methods how different driver sources check for the presence of the can_dma_32 field in the SCSI host template.
This issue is outside the scope of the current support status for RHEL2.1. No fix is planned.