its generally hard for the cpu to slow a disk down... On 12/11/2011, at 8:36 AM, Geoff Steckel wrote:
> Increasing MAXPHYS to 256K shows a few places where it's assumed that > there are 16 pages in MAXPHYS. > > In dev/ic/ahci.c I had to make this change @307 to make the > scatter-gather table large enough - 1 entry per page + extra > because that's what the previous code had and didn't say why. > I could understand +1 because a lot of code works that way. > > /* this makes ahci_cmd_table 512 bytes, supporting 128-byte alignment */ > /* #define AHCI_MAX_PRDT 24 too small for 256K of 4K pages */ > /* extra 12 is to match old 16 + 8 */ > #define AHCI_MAX_PRDT ((MAXPHYS / PAGE_SIZE) + 8) > > Grep-ing shows at least dev/ic/osiopvar.h doesn't compute > DMA resources from MAXPHYS. There are probably other "17"s buried > in ugly places. > > It doesn't seem to help disk I/O speed at all. > It *does* decrease interrupt rate to about 400/sec. > > Now to try some other tests. Grumble. > Geoff Steckel
