[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH for-4.13] x86/cpuid: Fix Lisbon/Magny-Cours Opterons WRT SSSE3/SSE4A
On 19.11.2019 18:00, Andrew Cooper wrote: > c/s ff66ccefe5 "x86/CPUID: adjust SSEn dependencies" made SSE4A depend on > SSSE3, but these processors really do have have SSE4A without SSSE3. > > This manifests as an upgrade regression, as the SSE4A feature disappears from > view. > > Adjust the SSE4A feature to depend on SSE3 rather than SSSE3. > > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> Nevertheless a remark: > --- a/xen/tools/gen-cpuid.py > +++ b/xen/tools/gen-cpuid.py > @@ -205,9 +205,10 @@ def crunch_numbers(state): > # than to SSE. > SSE2: [SSE3, LM, AESNI, PCLMULQDQ, SHA, GFNI], > > - # Other SSEn each depend on their predecessor versions. > - SSE3: [SSSE3], > - SSSE3: [SSE4_1, SSE4A], > + # Other SSEn each depend on their predecessor versions. AMD > + # Lisbon/Magny-Cours processors implemented SSE4A without SSSE3. > + SSE3: [SSSE3, SSE4A], > + SSSE3: [SSE4_1], > SSE4_1: [SSE4_2], If we'd be taking the SDM by the word, this would still be too restrictive. I suppose though it's been more a copy-and-paste effect that has lead to: "Before an application attempts to use the SIMD subset of SSE3 extensions, the application should follow the steps illustrated in Section 11.6.2, “Checking for SSE/SSE2 Support.” Next, use the additional step provided below: • Check that the processor supports the SIMD and x87 SSE3 extensions (if CPUID.01H:ECX.SSE3[bit 0] = 1)." "Before an application attempts to use the SSSE3 extensions, the application should follow the steps illustrated in Section 11.6.2, “Checking for SSE/SSE2 Support.” Next, use the additional step provided below: • Check that the processor supports SSSE3 (if CPUID.01H:ECX.SSSE3[bit 9] = 1)." Which would imply SSSE3 only takes SSE2 (and implicitly SSE) as prereq. As opposed: "Before an application attempts to use SSE4.1 instructions, the application should follow the steps illustrated in Section 11.6.2, “Checking for SSE/SSE2 Support.” Next, use the additional step provided below: Check that the processor supports SSE4.1 (if CPUID.01H:ECX.SSE4_1[bit 19] = 1), SSE3 (if CPUID.01H:ECX.SSE3[bit 0] = 1), and SSSE3 (if CPUID.01H:ECX.SSSE3[bit 9] = 1)." Similar text is there for for SSE4.2, taking additionally SSE4.1 as prereq. I'll fire off an email to Intel requesting clarification. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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