When executing guest vcpu-0 with FIFO:1 priority, which is necessary to deal with the following situation: VCPU-0 (housekeeping VCPU) VCPU-1 (realtime VCPU) raw_spin_lock(A) interrupted, schedule task T-1 raw_spin_lock(A) (spin) raw_spin_unlock(A) Certain operations must interrupt guest vcpu-0 (see trace below). To fix this issue, only change guest vcpu-0 to FIFO priority on spinlock critical sections (see patch). Hang trace ========== Without FIFO priority: qemu-kvm-6705 [002] ....1.. 767785.648964: kvm_exit: reason IO_INSTRUCTION rip 0xe8fe info 1f00039 0 qemu-kvm-6705 [002] ....1.. 767785.648965: kvm_exit: reason IO_INSTRUCTION rip 0xe911 info 3f60008 0 qemu-kvm-6705 [002] ....1.. 767785.648968: kvm_exit: reason IO_INSTRUCTION rip 0x8984 info 608000b 0 qemu-kvm-6705 [002] ....1.. 767785.648971: kvm_exit: reason IO_INSTRUCTION rip 0xb313 info 1f70008 0 qemu-kvm-6705 [002] ....1.. 767785.648974: kvm_exit: reason IO_INSTRUCTION rip 0xb514 info 3f60000 0 qemu-kvm-6705 [002] ....1.. 767785.648977: kvm_exit: reason PENDING_INTERRUPT rip 0x8052 info 0 0 qemu-kvm-6705 [002] ....1.. 767785.648980: kvm_exit: reason IO_INSTRUCTION rip 0xeee6 info 200040 0 qemu-kvm-6705 [002] ....1.. 767785.648999: kvm_exit: reason EPT_MISCONFIG rip 0x2120 info 0 0 With FIFO priority: qemu-kvm-7636 [002] ....1.. 768218.205065: kvm_exit: reason IO_INSTRUCTION rip 0xb313 info 1f70008 0 qemu-kvm-7636 [002] ....1.. 768218.205068: kvm_exit: reason IO_INSTRUCTION rip 0x8984 info 608000b 0 qemu-kvm-7636 [002] ....1.. 768218.205071: kvm_exit: reason IO_INSTRUCTION rip 0xb313 info 1f70008 0 qemu-kvm-7636 [002] ....1.. 768218.205074: kvm_exit: reason IO_INSTRUCTION rip 0x8984 info 608000b 0 qemu-kvm-7636 [002] ....1.. 768218.205077: kvm_exit: reason IO_INSTRUCTION rip 0xb313 info 1f70008 0 .. Performance numbers (kernel compilation with make -j2) ====================================================== With hypercall: 4:40. (make -j2) Without hypercall: 3:38. (make -j2) Note for NFV workloads spinlock performance is not relevant since DPDK should not enter the kernel (and housekeeping vcpu performance is far from a key factor). Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
