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 <[email protected]>
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;
}
-
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