RAID: add tilegx SIMD implementation of raid6

This change adds TILE-Gx SIMD instructions to the software raid
(md), modeling the Altivec implementation. This is only for Syndrome
generation; there is more that could be done to improve recovery,
as in the recent Intel SSE3 recovery implementation.

The code unrolls 8 times; this turns out to be the best on tilegx
hardware among the set 1, 2, 4, 8 or 16.  The code reads one
cache-line of data from each disk, stores P and Q then goes to the
next cache-line.

The test code in sys/linux/lib/raid6/test reports 2008 MB/s data
read rate for syndrome generation using 18 disks (16 data and 2
parity). It was 1512 MB/s before this SIMD optimizations. This is
running on 1 core with all the data in cache.

This is based on the paper The Mathematics of RAID-6.
(http://kernel.org/pub/linux/kernel/people/hpa/raid6.pdf).

Signed-off-by: Ken Steele <ken@tilera.com>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: NeilBrown <neilb@suse.de>

lib/raid6/test/Makefile

@@ -35,6 +35,9 @@ else
                 OBJS += altivec1.o altivec2.o altivec4.o altivec8.o
         endif
 endif
+ifeq ($(ARCH),tilegx)
+OBJS += tilegx8.o
+endif
 
 .c.o:
 	$(CC) $(CFLAGS) -c -o $@ $<
@@ -85,11 +88,15 @@ int16.c: int.uc ../unroll.awk
 int32.c: int.uc ../unroll.awk
 	$(AWK) ../unroll.awk -vN=32 < int.uc > $@
 
+tilegx8.c: tilegx.uc ../unroll.awk
+	$(AWK) ../unroll.awk -vN=8 < tilegx.uc > $@
+
 tables.c: mktables
 	./mktables > tables.c
 
 clean:
 	rm -f *.o *.a mktables mktables.c *.uc int*.c altivec*.c tables.c raid6test
+	rm -f tilegx*.c
 
 spotless: clean
 	rm -f *~