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x86: Fix Zen3/Zen4 ERMS selection (BZ 30994)

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The REP MOVSB usage on memcpy/memmove does not show much performance
improvement on Zen3/Zen4 cores compared to the vectorized loops.  Also,
as from BZ 30994, if the source is aligned and the destination is not
the performance can be 20x slower.

The performance difference is noticeable with small buffer sizes, closer
to the lower bounds limits when memcpy/memmove starts to use ERMS.  The
performance of REP MOVSB is similar to vectorized instruction on the
size limit (the L2 cache).  Also, there is no drawback to multiple cores
sharing the cache.

Checked on x86_64-linux-gnu on Zen3.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
This commit is contained in:
Adhemerval Zanella 2024-02-08 10:08:38 -03:00 committed by H.J. Lu
parent 155bb9d036
commit 0c0d39fe4a
1 changed files with 18 additions and 20 deletions
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38
sysdeps/x86/dl-cacheinfo.h
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@ -791,7 +791,6 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
long int data = -1;
long int shared = -1;
long int shared_per_thread = -1;
long int core = -1;
unsigned int threads = 0;
unsigned long int level1_icache_size = -1;
unsigned long int level1_icache_linesize = -1;
@ -809,7 +808,6 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
if (cpu_features->basic.kind == arch_kind_intel)
{
data = handle_intel (_SC_LEVEL1_DCACHE_SIZE, cpu_features);
core = handle_intel (_SC_LEVEL2_CACHE_SIZE, cpu_features);
shared = handle_intel (_SC_LEVEL3_CACHE_SIZE, cpu_features);
shared_per_thread = shared;
@ -822,7 +820,8 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
= handle_intel (_SC_LEVEL1_DCACHE_ASSOC, cpu_features);
level1_dcache_linesize
= handle_intel (_SC_LEVEL1_DCACHE_LINESIZE, cpu_features);
level2_cache_size = core;
level2_cache_size
= handle_intel (_SC_LEVEL2_CACHE_SIZE, cpu_features);
level2_cache_assoc
= handle_intel (_SC_LEVEL2_CACHE_ASSOC, cpu_features);
level2_cache_linesize
@ -835,12 +834,12 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
level4_cache_size
= handle_intel (_SC_LEVEL4_CACHE_SIZE, cpu_features);
get_common_cache_info (&shared, &shared_per_thread, &threads, core);
get_common_cache_info (&shared, &shared_per_thread, &threads,
level2_cache_size);
}
else if (cpu_features->basic.kind == arch_kind_zhaoxin)
{
data = handle_zhaoxin (_SC_LEVEL1_DCACHE_SIZE);
core = handle_zhaoxin (_SC_LEVEL2_CACHE_SIZE);
shared = handle_zhaoxin (_SC_LEVEL3_CACHE_SIZE);
shared_per_thread = shared;
@ -849,19 +848,19 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
level1_dcache_size = data;
level1_dcache_assoc = handle_zhaoxin (_SC_LEVEL1_DCACHE_ASSOC);
level1_dcache_linesize = handle_zhaoxin (_SC_LEVEL1_DCACHE_LINESIZE);
level2_cache_size = core;
level2_cache_size = handle_zhaoxin (_SC_LEVEL2_CACHE_SIZE);
level2_cache_assoc = handle_zhaoxin (_SC_LEVEL2_CACHE_ASSOC);
level2_cache_linesize = handle_zhaoxin (_SC_LEVEL2_CACHE_LINESIZE);
level3_cache_size = shared;
level3_cache_assoc = handle_zhaoxin (_SC_LEVEL3_CACHE_ASSOC);
level3_cache_linesize = handle_zhaoxin (_SC_LEVEL3_CACHE_LINESIZE);
get_common_cache_info (&shared, &shared_per_thread, &threads, core);
get_common_cache_info (&shared, &shared_per_thread, &threads,
level2_cache_size);
}
else if (cpu_features->basic.kind == arch_kind_amd)
{
data = handle_amd (_SC_LEVEL1_DCACHE_SIZE);
core = handle_amd (_SC_LEVEL2_CACHE_SIZE);
shared = handle_amd (_SC_LEVEL3_CACHE_SIZE);
level1_icache_size = handle_amd (_SC_LEVEL1_ICACHE_SIZE);
@ -869,7 +868,7 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
level1_dcache_size = data;
level1_dcache_assoc = handle_amd (_SC_LEVEL1_DCACHE_ASSOC);
level1_dcache_linesize = handle_amd (_SC_LEVEL1_DCACHE_LINESIZE);
level2_cache_size = core;
level2_cache_size = handle_amd (_SC_LEVEL2_CACHE_SIZE);;
level2_cache_assoc = handle_amd (_SC_LEVEL2_CACHE_ASSOC);
level2_cache_linesize = handle_amd (_SC_LEVEL2_CACHE_LINESIZE);
level3_cache_size = shared;
@ -880,12 +879,12 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
if (shared <= 0)
{
/* No shared L3 cache. All we have is the L2 cache. */
shared = core;
shared = level2_cache_size;
}
else if (cpu_features->basic.family < 0x17)
{
/* Account for exclusive L2 and L3 caches. */
shared += core;
shared += level2_cache_size;
}
shared_per_thread = shared;
@ -987,6 +986,12 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
if (CPU_FEATURE_USABLE_P (cpu_features, FSRM))
rep_movsb_threshold = 2112;
/* For AMD CPUs that support ERMS (Zen3+), REP MOVSB is in a lot of
cases slower than the vectorized path (and for some alignments,
it is really slow, check BZ #30994). */
if (cpu_features->basic.kind == arch_kind_amd)
rep_movsb_threshold = non_temporal_threshold;
/* The default threshold to use Enhanced REP STOSB. */
unsigned long int rep_stosb_threshold = 2048;
@ -1028,16 +1033,9 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
SIZE_MAX);
unsigned long int rep_movsb_stop_threshold;
/* ERMS feature is implemented from AMD Zen3 architecture and it is
performing poorly for data above L2 cache size. Henceforth, adding
an upper bound threshold parameter to limit the usage of Enhanced
REP MOVSB operations and setting its value to L2 cache size. */
if (cpu_features->basic.kind == arch_kind_amd)
rep_movsb_stop_threshold = core;
/* Setting the upper bound of ERMS to the computed value of
non-temporal threshold for architectures other than AMD. */
else
rep_movsb_stop_threshold = non_temporal_threshold;
non-temporal threshold for all architectures. */
rep_movsb_stop_threshold = non_temporal_threshold;
cpu_features->data_cache_size = data;
cpu_features->shared_cache_size = shared;