[ Upstream commit 9605505039 ]
The commit b2798ba0b8 ("KVM: X86: Choose qspinlock when dedicated
physical CPUs are available") states that when PV_DEDICATED=1
(vCPU has dedicated pCPU), qspinlock should be preferred regardless of
PV_UNHALT. However, the current implementation doesn't reflect this: when
PV_UNHALT=0, we still use virt_spin_lock() even with dedicated pCPUs.
This is suboptimal because:
1. Native qspinlocks should outperform virt_spin_lock() for dedicated
vCPUs irrespective of HALT exiting
2. virt_spin_lock() should only be preferred when vCPUs may be preempted
(non-dedicated case)
So reorder the PV spinlock checks to:
1. First handle dedicated pCPU case (disable virt_spin_lock_key)
2. Second check single CPU, and nopvspin configuration
3. Only then check PV_UNHALT support
This ensures we always use native qspinlock for dedicated vCPUs, delivering
pretty performance gains at high contention levels.
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Tested-by: Wangyang Guo <wangyang.guo@intel.com>
Link: https://lore.kernel.org/r/20250722110005.4988-1-lirongqing@baidu.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
b16a010338