aboutsummaryrefslogtreecommitdiff
path: root/arch/ia64/lib/do_csum.S
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/ia64/lib/do_csum.S
downloadlinux-stericsson-2.6.12-rc2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'arch/ia64/lib/do_csum.S')
-rw-r--r--arch/ia64/lib/do_csum.S323
1 files changed, 323 insertions, 0 deletions
diff --git a/arch/ia64/lib/do_csum.S b/arch/ia64/lib/do_csum.S
new file mode 100644
index 000000000000..6bec2fc9f5b2
--- /dev/null
+++ b/arch/ia64/lib/do_csum.S
@@ -0,0 +1,323 @@
+/*
+ *
+ * Optmized version of the standard do_csum() function
+ *
+ * Return: a 64bit quantity containing the 16bit Internet checksum
+ *
+ * Inputs:
+ * in0: address of buffer to checksum (char *)
+ * in1: length of the buffer (int)
+ *
+ * Copyright (C) 1999, 2001-2002 Hewlett-Packard Co
+ * Stephane Eranian <eranian@hpl.hp.com>
+ *
+ * 02/04/22 Ken Chen <kenneth.w.chen@intel.com>
+ * Data locality study on the checksum buffer.
+ * More optimization cleanup - remove excessive stop bits.
+ * 02/04/08 David Mosberger <davidm@hpl.hp.com>
+ * More cleanup and tuning.
+ * 01/04/18 Jun Nakajima <jun.nakajima@intel.com>
+ * Clean up and optimize and the software pipeline, loading two
+ * back-to-back 8-byte words per loop. Clean up the initialization
+ * for the loop. Support the cases where load latency = 1 or 2.
+ * Set CONFIG_IA64_LOAD_LATENCY to 1 or 2 (default).
+ */
+
+#include <asm/asmmacro.h>
+
+//
+// Theory of operations:
+// The goal is to go as quickly as possible to the point where
+// we can checksum 16 bytes/loop. Before reaching that point we must
+// take care of incorrect alignment of first byte.
+//
+// The code hereafter also takes care of the "tail" part of the buffer
+// before entering the core loop, if any. The checksum is a sum so it
+// allows us to commute operations. So we do the "head" and "tail"
+// first to finish at full speed in the body. Once we get the head and
+// tail values, we feed them into the pipeline, very handy initialization.
+//
+// Of course we deal with the special case where the whole buffer fits
+// into one 8 byte word. In this case we have only one entry in the pipeline.
+//
+// We use a (LOAD_LATENCY+2)-stage pipeline in the loop to account for
+// possible load latency and also to accommodate for head and tail.
+//
+// The end of the function deals with folding the checksum from 64bits
+// down to 16bits taking care of the carry.
+//
+// This version avoids synchronization in the core loop by also using a
+// pipeline for the accumulation of the checksum in resultx[] (x=1,2).
+//
+// wordx[] (x=1,2)
+// |---|
+// | | 0 : new value loaded in pipeline
+// |---|
+// | | - : in transit data
+// |---|
+// | | LOAD_LATENCY : current value to add to checksum
+// |---|
+// | | LOAD_LATENCY+1 : previous value added to checksum
+// |---| (previous iteration)
+//
+// resultx[] (x=1,2)
+// |---|
+// | | 0 : initial value
+// |---|
+// | | LOAD_LATENCY-1 : new checksum
+// |---|
+// | | LOAD_LATENCY : previous value of checksum
+// |---|
+// | | LOAD_LATENCY+1 : final checksum when out of the loop
+// |---|
+//
+//
+// See RFC1071 "Computing the Internet Checksum" for various techniques for
+// calculating the Internet checksum.
+//
+// NOT YET DONE:
+// - Maybe another algorithm which would take care of the folding at the
+// end in a different manner
+// - Work with people more knowledgeable than me on the network stack
+// to figure out if we could not split the function depending on the
+// type of packet or alignment we get. Like the ip_fast_csum() routine
+// where we know we have at least 20bytes worth of data to checksum.
+// - Do a better job of handling small packets.
+// - Note on prefetching: it was found that under various load, i.e. ftp read/write,
+// nfs read/write, the L1 cache hit rate is at 60% and L2 cache hit rate is at 99.8%
+// on the data that buffer points to (partly because the checksum is often preceded by
+// a copy_from_user()). This finding indiate that lfetch will not be beneficial since
+// the data is already in the cache.
+//
+
+#define saved_pfs r11
+#define hmask r16
+#define tmask r17
+#define first1 r18
+#define firstval r19
+#define firstoff r20
+#define last r21
+#define lastval r22
+#define lastoff r23
+#define saved_lc r24
+#define saved_pr r25
+#define tmp1 r26
+#define tmp2 r27
+#define tmp3 r28
+#define carry1 r29
+#define carry2 r30
+#define first2 r31
+
+#define buf in0
+#define len in1
+
+#define LOAD_LATENCY 2 // XXX fix me
+
+#if (LOAD_LATENCY != 1) && (LOAD_LATENCY != 2)
+# error "Only 1 or 2 is supported/tested for LOAD_LATENCY."
+#endif
+
+#define PIPE_DEPTH (LOAD_LATENCY+2)
+#define ELD p[LOAD_LATENCY] // end of load
+#define ELD_1 p[LOAD_LATENCY+1] // and next stage
+
+// unsigned long do_csum(unsigned char *buf,long len)
+
+GLOBAL_ENTRY(do_csum)
+ .prologue
+ .save ar.pfs, saved_pfs
+ alloc saved_pfs=ar.pfs,2,16,0,16
+ .rotr word1[4], word2[4],result1[LOAD_LATENCY+2],result2[LOAD_LATENCY+2]
+ .rotp p[PIPE_DEPTH], pC1[2], pC2[2]
+ mov ret0=r0 // in case we have zero length
+ cmp.lt p0,p6=r0,len // check for zero length or negative (32bit len)
+ ;;
+ add tmp1=buf,len // last byte's address
+ .save pr, saved_pr
+ mov saved_pr=pr // preserve predicates (rotation)
+(p6) br.ret.spnt.many rp // return if zero or negative length
+
+ mov hmask=-1 // initialize head mask
+ tbit.nz p15,p0=buf,0 // is buf an odd address?
+ and first1=-8,buf // 8-byte align down address of first1 element
+
+ and firstoff=7,buf // how many bytes off for first1 element
+ mov tmask=-1 // initialize tail mask
+
+ ;;
+ adds tmp2=-1,tmp1 // last-1
+ and lastoff=7,tmp1 // how many bytes off for last element
+ ;;
+ sub tmp1=8,lastoff // complement to lastoff
+ and last=-8,tmp2 // address of word containing last byte
+ ;;
+ sub tmp3=last,first1 // tmp3=distance from first1 to last
+ .save ar.lc, saved_lc
+ mov saved_lc=ar.lc // save lc
+ cmp.eq p8,p9=last,first1 // everything fits in one word ?
+
+ ld8 firstval=[first1],8 // load, ahead of time, "first1" word
+ and tmp1=7, tmp1 // make sure that if tmp1==8 -> tmp1=0
+ shl tmp2=firstoff,3 // number of bits
+ ;;
+(p9) ld8 lastval=[last] // load, ahead of time, "last" word, if needed
+ shl tmp1=tmp1,3 // number of bits
+(p9) adds tmp3=-8,tmp3 // effectively loaded
+ ;;
+(p8) mov lastval=r0 // we don't need lastval if first1==last
+ shl hmask=hmask,tmp2 // build head mask, mask off [0,first1off[
+ shr.u tmask=tmask,tmp1 // build tail mask, mask off ]8,lastoff]
+ ;;
+ .body
+#define count tmp3
+
+(p8) and hmask=hmask,tmask // apply tail mask to head mask if 1 word only
+(p9) and word2[0]=lastval,tmask // mask last it as appropriate
+ shr.u count=count,3 // how many 8-byte?
+ ;;
+ // If count is odd, finish this 8-byte word so that we can
+ // load two back-to-back 8-byte words per loop thereafter.
+ and word1[0]=firstval,hmask // and mask it as appropriate
+ tbit.nz p10,p11=count,0 // if (count is odd)
+ ;;
+(p8) mov result1[0]=word1[0]
+(p9) add result1[0]=word1[0],word2[0]
+ ;;
+ cmp.ltu p6,p0=result1[0],word1[0] // check the carry
+ cmp.eq.or.andcm p8,p0=0,count // exit if zero 8-byte
+ ;;
+(p6) adds result1[0]=1,result1[0]
+(p8) br.cond.dptk .do_csum_exit // if (within an 8-byte word)
+(p11) br.cond.dptk .do_csum16 // if (count is even)
+
+ // Here count is odd.
+ ld8 word1[1]=[first1],8 // load an 8-byte word
+ cmp.eq p9,p10=1,count // if (count == 1)
+ adds count=-1,count // loaded an 8-byte word
+ ;;
+ add result1[0]=result1[0],word1[1]
+ ;;
+ cmp.ltu p6,p0=result1[0],word1[1]
+ ;;
+(p6) adds result1[0]=1,result1[0]
+(p9) br.cond.sptk .do_csum_exit // if (count == 1) exit
+ // Fall through to caluculate the checksum, feeding result1[0] as
+ // the initial value in result1[0].
+ //
+ // Calculate the checksum loading two 8-byte words per loop.
+ //
+.do_csum16:
+ add first2=8,first1
+ shr.u count=count,1 // we do 16 bytes per loop
+ ;;
+ adds count=-1,count
+ mov carry1=r0
+ mov carry2=r0
+ brp.loop.imp 1f,2f
+ ;;
+ mov ar.ec=PIPE_DEPTH
+ mov ar.lc=count // set lc
+ mov pr.rot=1<<16
+ // result1[0] must be initialized in advance.
+ mov result2[0]=r0
+ ;;
+ .align 32
+1:
+(ELD_1) cmp.ltu pC1[0],p0=result1[LOAD_LATENCY],word1[LOAD_LATENCY+1]
+(pC1[1])adds carry1=1,carry1
+(ELD_1) cmp.ltu pC2[0],p0=result2[LOAD_LATENCY],word2[LOAD_LATENCY+1]
+(pC2[1])adds carry2=1,carry2
+(ELD) add result1[LOAD_LATENCY-1]=result1[LOAD_LATENCY],word1[LOAD_LATENCY]
+(ELD) add result2[LOAD_LATENCY-1]=result2[LOAD_LATENCY],word2[LOAD_LATENCY]
+2:
+(p[0]) ld8 word1[0]=[first1],16
+(p[0]) ld8 word2[0]=[first2],16
+ br.ctop.sptk 1b
+ ;;
+ // Since len is a 32-bit value, carry cannot be larger than a 64-bit value.
+(pC1[1])adds carry1=1,carry1 // since we miss the last one
+(pC2[1])adds carry2=1,carry2
+ ;;
+ add result1[LOAD_LATENCY+1]=result1[LOAD_LATENCY+1],carry1
+ add result2[LOAD_LATENCY+1]=result2[LOAD_LATENCY+1],carry2
+ ;;
+ cmp.ltu p6,p0=result1[LOAD_LATENCY+1],carry1
+ cmp.ltu p7,p0=result2[LOAD_LATENCY+1],carry2
+ ;;
+(p6) adds result1[LOAD_LATENCY+1]=1,result1[LOAD_LATENCY+1]
+(p7) adds result2[LOAD_LATENCY+1]=1,result2[LOAD_LATENCY+1]
+ ;;
+ add result1[0]=result1[LOAD_LATENCY+1],result2[LOAD_LATENCY+1]
+ ;;
+ cmp.ltu p6,p0=result1[0],result2[LOAD_LATENCY+1]
+ ;;
+(p6) adds result1[0]=1,result1[0]
+ ;;
+.do_csum_exit:
+ //
+ // now fold 64 into 16 bits taking care of carry
+ // that's not very good because it has lots of sequentiality
+ //
+ mov tmp3=0xffff
+ zxt4 tmp1=result1[0]
+ shr.u tmp2=result1[0],32
+ ;;
+ add result1[0]=tmp1,tmp2
+ ;;
+ and tmp1=result1[0],tmp3
+ shr.u tmp2=result1[0],16
+ ;;
+ add result1[0]=tmp1,tmp2
+ ;;
+ and tmp1=result1[0],tmp3
+ shr.u tmp2=result1[0],16
+ ;;
+ add result1[0]=tmp1,tmp2
+ ;;
+ and tmp1=result1[0],tmp3
+ shr.u tmp2=result1[0],16
+ ;;
+ add ret0=tmp1,tmp2
+ mov pr=saved_pr,0xffffffffffff0000
+ ;;
+ // if buf was odd then swap bytes
+ mov ar.pfs=saved_pfs // restore ar.ec
+(p15) mux1 ret0=ret0,@rev // reverse word
+ ;;
+ mov ar.lc=saved_lc
+(p15) shr.u ret0=ret0,64-16 // + shift back to position = swap bytes
+ br.ret.sptk.many rp
+
+// I (Jun Nakajima) wrote an equivalent code (see below), but it was
+// not much better than the original. So keep the original there so that
+// someone else can challenge.
+//
+// shr.u word1[0]=result1[0],32
+// zxt4 result1[0]=result1[0]
+// ;;
+// add result1[0]=result1[0],word1[0]
+// ;;
+// zxt2 result2[0]=result1[0]
+// extr.u word1[0]=result1[0],16,16
+// shr.u carry1=result1[0],32
+// ;;
+// add result2[0]=result2[0],word1[0]
+// ;;
+// add result2[0]=result2[0],carry1
+// ;;
+// extr.u ret0=result2[0],16,16
+// ;;
+// add ret0=ret0,result2[0]
+// ;;
+// zxt2 ret0=ret0
+// mov ar.pfs=saved_pfs // restore ar.ec
+// mov pr=saved_pr,0xffffffffffff0000
+// ;;
+// // if buf was odd then swap bytes
+// mov ar.lc=saved_lc
+//(p15) mux1 ret0=ret0,@rev // reverse word
+// ;;
+//(p15) shr.u ret0=ret0,64-16 // + shift back to position = swap bytes
+// br.ret.sptk.many rp
+
+END(do_csum)