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cpuid_zarch/hwcaps: add documentation and dump hwcaps in init 

Add pointers to the definition of the hardware capability flags in glibc
and describe how they relate to the levels CPU_Z13 and CPU_Z14 for
optimized kernels.

To aid identifying available hardware capabilities and in debugging
potential build issues, dump their value in dynamic_arch_init() when
OPENBLAS_VERBOSE is set to 2 or higher.

Signed-off-by: Marius Hillenbrand <mhillen@linux.ibm.com>
This commit is contained in:
Marius Hillenbrand 2021-10-27 17:26:28 +02:00
parent aa231b5875
commit 77747bc536
2 changed files with 45 additions and 3 deletions
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34
cpuid_zarch.h
View File

@ -56,6 +56,40 @@ static int detect(void)
{
unsigned long hwcap = get_hwcap();
// Choose the architecture level for optimized kernels based on hardware
// capability bits (just like glibc chooses optimized implementations).
//
// The hardware capability bits that are used here indicate both
// hardware support for a particular ISA extension and the presence of
// software support to enable its use. For example, when HWCAP_S390_VX
// is set then both the CPU can execute SIMD instructions and the Linux
// kernel can manage applications using the vector registers and SIMD
// instructions.
//
// See glibc's sysdeps/s390/dl-procinfo.h for an overview (also in
// sysdeps/unix/sysv/linux/s390/bits/hwcap.h) of the defined hardware
// capability bits. They are derived from the information that the
// "store facility list (extended)" instructions provide.
// (https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=sysdeps/s390/dl-procinfo.h;hb=HEAD)
//
// currently used:
// HWCAP_S390_VX - vector facility for z/Architecture (introduced with
// IBM z13), enables level CPU_Z13 (SIMD)
// HWCAP_S390_VXE - vector enhancements facility 1 (introduced with IBM
// z14), together with VX enables level CPU_Z14
// (single-precision SIMD instructions)
//
// When you add optimized kernels that make use of other ISA extensions
// (e.g., for exploiting the vector-enhancements facility 2 that was introduced
// with IBM z15), then add a new architecture level (e.g., CPU_Z15) and gate
// it on the hwcap that represents it here (e.g., HWCAP_S390_VXRS_EXT2
// for the z15 vector enhancements).
//
// To learn the value of hwcaps on a given system, set the environment
// variable LD_SHOW_AUXV and let ld.so dump it (e.g., by running
// LD_SHOW_AUXV=1 /bin/true).
// Also, the init function for dynamic arch support will print hwcaps
// when OPENBLAS_VERBOSE is set to 2 or higher.
if ((hwcap & HWCAP_S390_VX) && (hwcap & HWCAP_S390_VXE))
return CPU_Z14;

14
driver/others/dynamic_zarch.c
View File

@ -13,6 +13,7 @@ extern gotoblas_t gotoblas_Z14;
#define NUM_CORETYPES 4
extern int openblas_verbose();
extern void openblas_warning(int verbose, const char* msg);
char* gotoblas_corename(void) {
@ -120,6 +121,11 @@ void gotoblas_dynamic_init(void) {
else
{
gotoblas = get_coretype();
if (openblas_verbose() >= 2) {
snprintf(coremsg, sizeof(coremsg), "Choosing kernels based on getauxval(AT_HWCAP)=0x%lx\n",
getauxval(AT_HWCAP));
openblas_warning(2, coremsg);
}
}
if (gotoblas == NULL)
@ -130,9 +136,11 @@ void gotoblas_dynamic_init(void) {
}
if (gotoblas && gotoblas->init) {
strncpy(coren, gotoblas_corename(), 20);
sprintf(coremsg, "Core: %s\n", coren);
openblas_warning(2, coremsg);
if (openblas_verbose() >= 2) {
strncpy(coren, gotoblas_corename(), 20);
sprintf(coremsg, "Core: %s\n", coren);
openblas_warning(2, coremsg);
}
gotoblas->init();
}
else {