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[FFmpeg-devel,03/11] avutil: detect when AVX-512 is available

Message ID 20171109115837.32618-4-jdarnley@obe.tv
State Superseded
Headers show

Commit Message

James Darnley Nov. 9, 2017, 11:58 a.m. UTC 
---
I've changed this patch slightly because I discovered that it would cause an
illegal instruction exception on much older processors (probably all without
AVX).  I was running xgetbv() almost uncontitionally.  Now it is a little more
like what is the in x264 patch.

 libavutil/x86/cpu.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

James Darnley Nov. 20, 2017, 11:21 a.m. UTC | #1 
On 2017-11-10 03:11, James Almer wrote:
> On 11/9/2017 8:58 AM, James Darnley wrote:
>> @@ -154,6 +155,13 @@ int ff_get_cpu_flags_x86(void)
>>              if (ebx & 0x00000100)
>>                  rval |= AV_CPU_FLAG_BMI2;
>>          }
>> +#if HAVE_AVX512 /* F, CD, BW, DQ, VL */
> 
> Nit: Maybe move this chunk inside the HAVE_AVX2 block, at the end of it,
> right above the BMI checks.

I am preparing a final patch set and I forgot to ask you this at the
time.  Do you want me to put the new check inside the AVX2 if(){} block
too? Or just in the preprocessor #if #endif?

>> +        if ((xcr0_lo & 0xe6) == 0xe6) {
> 
> Nit: The proper check here i think would be
> 
> if ((xcr0_lo & 0xe0) == 0xe0) {
>     if ((rval & AV_CPU_FLAG_AVX) && (ebx & 0xd0030000) == 0xd0030000)
>         rval |= AV_CPU_FLAG_AVX512;
> }
> 
> But it's functionally the same.

Ah.  Make it dependent on previous checks that have already checked for
features.  Did you mean AVX or AVX2 in this "(rval & AV_CPU_FLAG_AVX)"?
diff mbox

Patch

diff --git a/libavutil/x86/cpu.c b/libavutil/x86/cpu.c
index f33088c8c7..589fdef7da 100644
--- a/libavutil/x86/cpu.c
+++ b/libavutil/x86/cpu.c
@@ -97,6 +97,7 @@  int ff_get_cpu_flags_x86(void)
     int max_std_level, max_ext_level, std_caps = 0, ext_caps = 0;
     int family = 0, model = 0;
     union { int i[3]; char c[12]; } vendor;
+    int xcr0_lo = 0, xcr0_hi = 0;
 
     if (!cpuid_test())
         return 0; /* CPUID not supported */
@@ -132,8 +133,8 @@  int ff_get_cpu_flags_x86(void)
         /* Check OXSAVE and AVX bits */
         if ((ecx & 0x18000000) == 0x18000000) {
             /* Check for OS support */
-            xgetbv(0, eax, edx);
-            if ((eax & 0x6) == 0x6) {
+            xgetbv(0, xcr0_lo, xcr0_hi);
+            if ((xcr0_lo & 0x6) == 0x6) {
                 rval |= AV_CPU_FLAG_AVX;
                 if (ecx & 0x00001000)
                     rval |= AV_CPU_FLAG_FMA3;
@@ -154,6 +155,13 @@  int ff_get_cpu_flags_x86(void)
             if (ebx & 0x00000100)
                 rval |= AV_CPU_FLAG_BMI2;
         }
+#if HAVE_AVX512 /* F, CD, BW, DQ, VL */
+        if ((xcr0_lo & 0xe6) == 0xe6) {
+            if ((ebx & 0xd0030000) == 0xd0030000)
+                rval |= AV_CPU_FLAG_AVX512;
+
+        }
+#endif
     }
 
     cpuid(0x80000000, max_ext_level, ebx, ecx, edx);