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# x86 specific tunables.
# Copyright (C) 2017-2024 Free Software Foundation, Inc.
# This file is part of the GNU C Library.
# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# <https://www.gnu.org/licenses/>.
glibc {
cpu {
hwcaps {
type: STRING
}
x86_ibt {
type: STRING
}
x86_shstk {
type: STRING
}
x86_non_temporal_threshold {
type: SIZE_T
}
x86_rep_movsb_threshold {
type: SIZE_T
# Since there is overhead to set up REP MOVSB operation, REP
# MOVSB isn't faster on short data. The memcpy micro benchmark
# in glibc shows that 2KB is the approximate value above which
# REP MOVSB becomes faster than SSE2 optimization on processors
# with Enhanced REP MOVSB. Since larger register size can move
# more data with a single load and store, the threshold is
# higher with larger register size. Micro benchmarks show AVX
# REP MOVSB becomes faster apprximately at 8KB. The AVX512
# threshold is extrapolated to 16KB. For machines with FSRM the
# threshold is universally set at 2112 bytes. Note: Since the
# REP MOVSB threshold must be greater than 8 times of vector
# size and the default value is 4096 * (vector size / 16), the
# default value and the minimum value must be updated at
# run-time. NB: Don't set the default value since we can't tell
# if the tunable value is set by user or not [BZ #27069].
minval: 1
}
x86_rep_stosb_threshold {
type: SIZE_T
# Since there is overhead to set up REP STOSB operation, REP STOSB
# isn't faster on short data. The memset micro benchmark in glibc
# shows that 2KB is the approximate value above which REP STOSB
# becomes faster on processors with Enhanced REP STOSB. Since the
# stored value is fixed, larger register size has minimal impact
# on threshold.
minval: 1
default: 2048
}
x86_data_cache_size {
type: SIZE_T
}
x86_shared_cache_size {
type: SIZE_T
}
plt_rewrite {
type: INT_32
minval: 0
maxval: 2
}
}
}
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