/* * * 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 * * 02/04/22 Ken Chen * Data locality study on the checksum buffer. * More optimization cleanup - remove excessive stop bits. * 02/04/08 David Mosberger * More cleanup and tuning. * 01/04/18 Jun Nakajima * 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 // // 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 accomodate 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 // intialize 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)