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Ship it! Ship It! - Jason Lowe-Power On Jan. 23, 2017, 3:39 p.m., Santi Galan wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > http://reviews.gem5.org/r/3790/ > ----------------------------------------------------------- > > (Updated Jan. 23, 2017, 3:39 p.m.) > > > Review request for Default. > > > Repository: gem5 > > > Description > ------- > > Changeset 11801:80af6a1e6beb > \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- > x86: fixed branching() computation for branch uops that only changes nupc and > not npc > > When a branch micro-op belongs to a flow and the micro-op does not change the > nPC and just updates the nuPC > (like a 'rep movs' flow), `branching()` function always returns not-taken no > matter actual > micro-branch outcome. Provided fix adds to the equation nuPC attribute > checking since these kind of branch > micro-op only updates that pointer. > > This issue has been found while debugging the performance of a copy-loop > implemented with `memcopy` function. Without the fix, 'rep movss' internal > micro-branch was always predicted as not-taken causing an squash event after > every branch micro-branch execution. > > Using the provided test, branch mispredition went from *1922* without the fix > to *7*. > > > Diffs > ----- > > src/arch/x86/types.hh e47703369039 > > Diff: http://reviews.gem5.org/r/3790/diff/ > > > Testing > ------- > > I used this command line to evaluate the performance: > > ``` > ./build/X86/gem5.opt configs/example/se.py --cpu-type=detailed --caches > --l2cache -c /path/to/binary > ``` > > This is the source code of the binary: > ``` > #include <string.h> > #include "m5op.h" > > #define SIZE 15*1024 > > //arrays are cache aligned > char a [SIZE] __attribute__((aligned(0x40))); > char b [SIZE] __attribute__((aligned(0x40))); > > int main () > { > //some warmup > int i; > for (i = 0; i < SIZE; ++i) > { > a[i] = 1; > b[i] = 2; > } > > m5_reset_stats(0, 0); > memcpy(a, b, SIZE); > m5_exit(0); > > //keep compiler happy > return 0; > } > ``` > > Which was compiled with this makefile: > > ``` > GEM5_PATH=/path/to/gem5 > > binary: binary.c $(GEM5_PATH)/util/m5/m5op_x86.S > gcc -o $@ $^ -static -I$(GEM5_PATH)/util/m5 > ``` > > > Thanks, > > Santi Galan > > _______________________________________________ gem5-dev mailing list gem5-dev@gem5.org http://m5sim.org/mailman/listinfo/gem5-dev
