Hi Babu,
On Wed, Aug 02, 2023 at 10:41:17AM -0500, Moger, Babu wrote:
> Date: Wed, 2 Aug 2023 10:41:17 -0500
> From: "Moger, Babu" <[email protected]>
> Subject: Re: [PATCH v3 05/17] i386/cpu: Use APIC ID offset to encode cache
> topo in CPUID[4]
>
> Hi Zhao,
>
> On 8/1/23 05:35, Zhao Liu wrote:
> > From: Zhao Liu <[email protected]>
> >
> > Refer to the fixes of cache_info_passthrough ([1], [2]) and SDM, the
> > CPUID.04H:EAX[bits 25:14] and CPUID.04H:EAX[bits 31:26] should use the
> > nearest power-of-2 integer.
> >
> > The nearest power-of-2 integer can be caculated by pow2ceil() or by
> > using APIC ID offset (like L3 topology using 1 << die_offset [3]).
> >
> > But in fact, CPUID.04H:EAX[bits 25:14] and CPUID.04H:EAX[bits 31:26]
> > are associated with APIC ID. For example, in linux kernel, the field
> > "num_threads_sharing" (Bits 25 - 14) is parsed with APIC ID. And for
> > another example, on Alder Lake P, the CPUID.04H:EAX[bits 31:26] is not
> > matched with actual core numbers and it's caculated by:
> > "(1 << (pkg_offset - core_offset)) - 1".
> >
> > Therefore the offset of APIC ID should be preferred to caculate nearest
> > power-of-2 integer for CPUID.04H:EAX[bits 25:14] and CPUID.04H:EAX[bits
> > 31:26]:
> > 1. d/i cache is shared in a core, 1 << core_offset should be used
> > instand of "cs->nr_threads" in encode_cache_cpuid4() for
> > CPUID.04H.00H:EAX[bits 25:14] and CPUID.04H.01H:EAX[bits 25:14].
> > 2. L2 cache is supposed to be shared in a core as for now, thereby
> > 1 << core_offset should also be used instand of "cs->nr_threads" in
> > encode_cache_cpuid4() for CPUID.04H.02H:EAX[bits 25:14].
> > 3. Similarly, the value for CPUID.04H:EAX[bits 31:26] should also be
> > replaced by the offsets upper SMT level in APIC ID.
> >
> > In addition, use APIC ID offset to replace "pow2ceil()" for
> > cache_info_passthrough case.
> >
> > [1]: efb3934adf9e ("x86: cpu: make sure number of addressable IDs for
> > processor cores meets the spec")
> > [2]: d7caf13b5fcf ("x86: cpu: fixup number of addressable IDs for logical
> > processors sharing cache")
> > [3]: d65af288a84d ("i386: Update new x86_apicid parsing rules with
> > die_offset support")
> >
> > Fixes: 7e3482f82480 ("i386: Helpers to encode cache information
> > consistently")
> > Suggested-by: Robert Hoo <[email protected]>
> > Signed-off-by: Zhao Liu <[email protected]>
> > ---
> > Changes since v1:
> > * Use APIC ID offset to replace "pow2ceil()" for cache_info_passthrough
> > case. (Yanan)
> > * Split the L1 cache fix into a separate patch.
> > * Rename the title of this patch (the original is "i386/cpu: Fix number
> > of addressable IDs in CPUID.04H").
> > ---
> > target/i386/cpu.c | 30 +++++++++++++++++++++++-------
> > 1 file changed, 23 insertions(+), 7 deletions(-)
> >
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index b439a05244ee..c80613bfcded 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -6005,7 +6005,6 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> > uint32_t count,
> > {
> > X86CPU *cpu = env_archcpu(env);
> > CPUState *cs = env_cpu(env);
> > - uint32_t die_offset;
> > uint32_t limit;
> > uint32_t signature[3];
> > X86CPUTopoInfo topo_info;
> > @@ -6089,39 +6088,56 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t
> > index, uint32_t count,
> > int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14);
> > int vcpus_per_socket = cs->nr_cores * cs->nr_threads;
> > if (cs->nr_cores > 1) {
> > + int addressable_cores_offset =
> > +
> > apicid_pkg_offset(&topo_info) -
> > +
> > apicid_core_offset(&topo_info);
> > +
> > *eax &= ~0xFC000000;
> > - *eax |= (pow2ceil(cs->nr_cores) - 1) << 26;
> > + *eax |= (1 << addressable_cores_offset - 1) << 26;
> > }
> > if (host_vcpus_per_cache > vcpus_per_socket) {
> > + int pkg_offset = apicid_pkg_offset(&topo_info);
> > +
> > *eax &= ~0x3FFC000;
> > - *eax |= (pow2ceil(vcpus_per_socket) - 1) << 14;
> > + *eax |= (1 << pkg_offset - 1) << 14;
> > }
> > }
>
> I hit this compile error with this patch.
>
> [1/18] Generating qemu-version.h with a custom command (wrapped by meson
> to capture output)
> [2/4] Compiling C object libqemu-x86_64-softmmu.fa.p/target_i386_cpu.c.o
> FAILED: libqemu-x86_64-softmmu.fa.p/target_i386_cpu.c.o
> ..
> ..
> softmmu.fa.p/target_i386_cpu.c.o -c ../target/i386/cpu.c
> ../target/i386/cpu.c: In function ‘cpu_x86_cpuid’:
> ../target/i386/cpu.c:6096:60: error: suggest parentheses around ‘-’ inside
> ‘<<’ [-Werror=parentheses]
> 6096 | *eax |= (1 << addressable_cores_offset - 1) << 26;
> | ~~~~~~~~~~~~~~~~~~~~~~~~~^~~
> ../target/i386/cpu.c:6102:46: error: suggest parentheses around ‘-’ inside
> ‘<<’ [-Werror=parentheses]
> 6102 | *eax |= (1 << pkg_offset - 1) << 14;
> | ~~~~~~~~~~~^~~
> cc1: all warnings being treated as errors
>
> Please fix this.
Thanks for your test! Sorry I may miss this warning. I'll fix this.
Thanks,
Zhao
>
>
> > } else if (cpu->vendor_cpuid_only && IS_AMD_CPU(env)) {
> > *eax = *ebx = *ecx = *edx = 0;
> > } else {
> > *eax = 0;
> > + int addressable_cores_offset = apicid_pkg_offset(&topo_info) -
> > + apicid_core_offset(&topo_info);
> > + int core_offset, die_offset;
> > +
> > switch (count) {
> > case 0: /* L1 dcache info */
> > + core_offset = apicid_core_offset(&topo_info);
> > encode_cache_cpuid4(env->cache_info_cpuid4.l1d_cache,
> > - cs->nr_threads, cs->nr_cores,
> > + (1 << core_offset),
> > + (1 << addressable_cores_offset),
> > eax, ebx, ecx, edx);
> > break;
> > case 1: /* L1 icache info */
> > + core_offset = apicid_core_offset(&topo_info);
> > encode_cache_cpuid4(env->cache_info_cpuid4.l1i_cache,
> > - cs->nr_threads, cs->nr_cores,
> > + (1 << core_offset),
> > + (1 << addressable_cores_offset),
> > eax, ebx, ecx, edx);
> > break;
> > case 2: /* L2 cache info */
> > + core_offset = apicid_core_offset(&topo_info);
> > encode_cache_cpuid4(env->cache_info_cpuid4.l2_cache,
> > - cs->nr_threads, cs->nr_cores,
> > + (1 << core_offset),
> > + (1 << addressable_cores_offset),
> > eax, ebx, ecx, edx);
> > break;
> > case 3: /* L3 cache info */
> > die_offset = apicid_die_offset(&topo_info);
> > if (cpu->enable_l3_cache) {
> > encode_cache_cpuid4(env->cache_info_cpuid4.l3_cache,
> > - (1 << die_offset), cs->nr_cores,
> > + (1 << die_offset),
> > + (1 << addressable_cores_offset),
> > eax, ebx, ecx, edx);
> > break;
> > }
>
> --
> Thanks
> Babu Moger
