Use an independently-formatted "unsigned int" for data instead of a restrictive "u16" to avoid instruction fetch pipeline stalls probably caused by the byte calculations later. ide_end_drive_cmd() uses an u16 variable for the result of an INW() which it then does some byte masking operations on. On my P3/700, this results in a highly visible IFU_MEM_STALL oprofile blip when doing a simple "load 30 larger GUI apps in parallel" benchmark (which takes about 1:30 or so, BTW): The ide_end_drive_cmd() IFU_MEM_STALL amounts to 0.59% of all IFU_MEM_STALL events during the profiling, with this opcode line amounting to > 95% IFU_MEM_STALL within the function itself. Replacing the u16 by an architecture-independently formatted unsigned int to ease the byte-masking operations: /* no u16 here: caused severe IFU_MEM_STALL! */ unsigned int data = hwif->INW(IDE_DATA_REG); args->tfRegister[IDE_DATA_OFFSET] = (data) & 0xFF; args->hobRegister[IDE_DATA_OFFSET] = (data >> 8) & 0xFF; completely puts ide_end_drive_cmd() off the IFU_MEM_STALL radar during repeated profiling attempts (after a fresh reboot with the modified kernel), as opposed to having been the *top* oprofile trace item before. I suppose that this is something like a textbook example of why it's sometimes not beneficial to not use native-sized (i.e., 32bit) variables, right? Run-tested on 2.6.17-mm4. Signed-off-by: Andreas Mohr <andi@xxxxxxxx> diff -urN linux-2.6.17-mm4.orig/drivers/ide/ide-io.c linux-2.6.17-mm4.my/drivers/ide/ide-io.c --- linux-2.6.17-mm4.orig/drivers/ide/ide-io.c 2006-06-29 11:57:12.000000000 +0200 +++ linux-2.6.17-mm4.my/drivers/ide/ide-io.c 2006-06-30 11:54:12.000000000 +0200 @@ -397,7 +397,8 @@ if (args) { if (args->tf_in_flags.b.data) { - u16 data = hwif->INW(IDE_DATA_REG); + /* no u16 here: caused severe IFU_MEM_STALL! */ + unsigned int data = hwif->INW(IDE_DATA_REG); args->tfRegister[IDE_DATA_OFFSET] = (data) & 0xFF; args->hobRegister[IDE_DATA_OFFSET] = (data >> 8) & 0xFF; } - : send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html