1 # x86 specific tunables.
2 # Copyright (C) 2017-2022 Free Software Foundation, Inc.
3 # This file is part of the GNU C Library.
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30 x86_non_temporal_threshold {
33 x86_rep_movsb_threshold {
35 # Since there is overhead to set up REP MOVSB operation, REP
36 # MOVSB isn't faster on short data. The memcpy micro benchmark
37 # in glibc shows that 2KB is the approximate value above which
38 # REP MOVSB becomes faster than SSE2 optimization on processors
39 # with Enhanced REP MOVSB. Since larger register size can move
40 # more data with a single load and store, the threshold is
41 # higher with larger register size. Micro benchmarks show AVX
42 # REP MOVSB becomes faster apprximately at 8KB. The AVX512
43 # threshold is extrapolated to 16KB. For machines with FSRM the
44 # threshold is universally set at 2112 bytes. Note: Since the
45 # REP MOVSB threshold must be greater than 8 times of vector
46 # size and the default value is 4096 * (vector size / 16), the
47 # default value and the minimum value must be updated at
48 # run-time. NB: Don't set the default value since we can't tell
49 # if the tunable value is set by user or not [BZ #27069].
52 x86_rep_stosb_threshold {
54 # Since there is overhead to set up REP STOSB operation, REP STOSB
55 # isn't faster on short data. The memset micro benchmark in glibc
56 # shows that 2KB is the approximate value above which REP STOSB
57 # becomes faster on processors with Enhanced REP STOSB. Since the
58 # stored value is fixed, larger register size has minimal impact
66 x86_shared_cache_size {