diff options
Diffstat (limited to 'sysdeps/x86/dl-tunables.list')
| -rw-r--r-- | sysdeps/x86/dl-tunables.list | 26 |
1 files changed, 15 insertions, 11 deletions
diff --git a/sysdeps/x86/dl-tunables.list b/sysdeps/x86/dl-tunables.list index dd6e1d65c9..419313804d 100644 --- a/sysdeps/x86/dl-tunables.list +++ b/sysdeps/x86/dl-tunables.list @@ -32,17 +32,21 @@ glibc { } 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. Note: Since the REP MOVSB threshold must be greater than 8 - # times of vector size and the default value is 2048 * (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]. + # 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 { |