Re: flush_icache_range

Zoltan Menyhart
2005-05-23T13:43:16Z

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The Itanium 2 processor Reference Manual for SW development & optimization
(May 2004) says in the chapter 5.8:

"In Itanium 2 processor, each fc will invalidate 128 bytes corresponding
to the L3 cache line size. Since both the L1I and L1D have line sizes of
64 bytes, a single fc instruction can invalidate two lines."

Can someone please confirm that an equivalent statement is true for the
"fc.i", too ?
Say:

"In Itanium 2 processor, each fc.i instruction will ensure that 128 bytes
(corresponding to the L3 cache line size) of the I-cache(s) be coherent with
the data caches. Since the L1I cache has line sizes of 64 bytes, a single
fc.i instruction can make coherent two lines."

This gave me the idea to try with 128-byte strides
(the measures are repeated for 10 times):

Modified in d-cache:
cycles = 19,164 time = 14.782 usec
cycles = 18,060 time = 13.930 usec
cycles = 16,929 time = 13.058 usec
cycles = 17,597 time = 13.573 usec
cycles = 17,163 time = 13.239 usec
cycles = 16,990 time = 13.105 usec
cycles = 17,427 time = 13.442 usec
cycles = 17,028 time = 13.134 usec
cycles = 16,993 time = 13.107 usec
cycles = 16,930 time = 13.059 usec

Valid:
cycles = 13,514 time = 10.424 usec
cycles = 13,518 time = 10.427 usec
cycles = 13,518 time = 10.427 usec
cycles = 13,518 time = 10.427 usec
cycles = 13,518 time = 10.427 usec
cycles = 13,746 time = 10.603 usec
cycles = 13,866 time = 10.695 usec
cycles = 13,830 time = 10.668 usec
cycles = 13,790 time = 10.637 usec
cycles = 13,830 time = 10.668 usec

Invalid:
cycles = 13,794 time = 10.640 usec
cycles = 13,790 time = 10.637 usec
cycles = 13,830 time = 10.668 usec
cycles = 13,830 time = 10.668 usec
cycles = 13,966 time = 10.773 usec
cycles = 13,994 time = 10.794 usec
cycles = 14,074 time = 10.856 usec
cycles = 13,574 time = 10.470 usec
cycles = 13,902 time = 10.723 usec
cycles = 14,114 time = 10.887 usec

I got these incredibly low number of cycles,
compared to my previous results:

With a 32-byte stride:

Modified in d-cache: cycles = 215 K, time = 169 usec
Valid: cycles = 222 K, time = 171 usec
Invalid: cycles = 222 K, time = 171 usec

With a 64-byte stride:

Modified in d-cache: cycles = 63 K, time = 49 usec
Valid: cycles = 116 K, time = 89 usec
Invalid: cycles = 116 K, time = 89 usec

This is a Tiger box with the following CPUs:
processor : 0
vendor : GenuineIntel
arch : IA-64
family : Itanium 2
model : 1
revision : 5
archrev : 0
features : branchlong
cpu number : 0
cpu regs : 4
cpu MHz : 1296.435998
itc MHz : 1296.435998
BogoMIPS : 1941.96
etc...

Can these results be real?

Thanks,

Zoltan

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--- linux-2.6.11-orig/arch/ia64/lib/flush.S 2005-04-26 15:59:49.000000000 +0200
+++ linux-2.6.11/arch/ia64/lib/flush.S 2005-05-23 15:30:24.891935385 +0200
@@ -7,6 +7,22 @@
#include <asm/asmmacro.h>
#include <asm/page.h>

+
+#if defined(CONFIG_ITANIUM)
+#define CACHE_SHIFT 5
+#else
+/*
+ * In Itanium 2 processor, each fc.i instruction will ensure that 128 bytes
+ * (corresponding to the L3 cache line size) of the I-cache(s) be coherent with
+ * the data caches. Since the L1I cache has line sizes of 64 bytes, a single
+ * fc.i instruction can make coherent two lines.
+ */
+#define CACHE_SHIFT 7
+#endif
+
+#define CACHE_BYTES (1 << CACHE_SHIFT)
+
+
/*
* flush_icache_range(start,end)
* Must flush range from start to end-1 but nothing else (need to
@@ -17,7 +33,7 @@
alloc r2=ar.pfs,2,0,0,0
sub r8=in1,in0,1
;;
- shr.u r8=r8,5 // we flush 32 bytes per iteration
+ shr.u r8=r8,CACHE_SHIFT // we flush CACHE_BYTES bytes per iteration
.save ar.lc, r3
mov r3=ar.lc // save ar.lc
;;
@@ -26,8 +42,8 @@

mov ar.lc=r8
;;
-.Loop: fc in0 // issuable on M0 only
- add in0=32,in0
+.Loop: fc.i in0 // issuable on M0 only
+ add in0=CACHE_BYTES,in0
br.cloop.sptk.few .Loop
;;
sync.i