On 27.02.2025 09:25, Zhao Liu wrote:
From: Chuang Xu <xuchuangxc...@bytedance.com>
When QEMU is started with:
-cpu host,migratable=on,host-cache-info=on,l3-cache=off
-smp 180,sockets=2,dies=1,cores=45,threads=2
On Intel platform:
CPUID.01H.EBX[23:16] is defined as "max number of addressable IDs for
logical processors in the physical package".
When executing "cpuid -1 -l 1 -r" in the guest, we obtain a value of 90 for
CPUID.01H.EBX[23:16], whereas the expected value is 128. Additionally,
executing "cpuid -1 -l 4 -r" in the guest yields a value of 63 for
CPUID.04H.EAX[31:26], which matches the expected result.
As (1+CPUID.04H.EAX[31:26]) rounds up to the nearest power-of-2 integer,
it's necessary to round up CPUID.01H.EBX[23:16] to the nearest power-of-2
integer too. Otherwise there would be unexpected results in guest with
older kernel.
For example, when QEMU is started with CLI above and xtopology is disabled,
guest kernel 5.15.120 uses CPUID.01H.EBX[23:16]/(1+CPUID.04H.EAX[31:26]) to
calculate threads-per-core in detect_ht(). Then guest will get "90/(1+63)=1"
as the result, even though threads-per-core should actually be 2.
And on AMD platform:
CPUID.01H.EBX[23:16] is defined as "Logical processor count". Current
result meets our expectation.
So round up CPUID.01H.EBX[23:16] to the nearest power-of-2 integer only
for Intel platform to solve the unexpected result.
This change doesn't need to add compat property since it does not affect
live migration between different versions of pc machines.
Cc: qemu-sta...@nongnu.org
Reviewed-by: Zhao Liu <zhao1....@intel.com>
Acked-by: Igor Mammedov <imamm...@redhat.com>
Signed-off-by: Guixiong Wei <weiguixi...@bytedance.com>
Signed-off-by: Yipeng Yin <yinyip...@bytedance.com>
Signed-off-by: Chuang Xu <xuchuangxc...@bytedance.com>
Signed-off-by: Zhao Liu <zhao1....@intel.com>
Ping?
Is this series still needed ?
Thanks,
/mjt
