On Wed, Feb 08, 2017 at 01:00:24PM -0500, Waiman Long wrote: > It was found when running fio sequential write test with a XFS ramdisk > on a 2-socket x86-64 system, the %CPU times as reported by perf were > as follows: > > 71.27% 0.28% fio [k] down_write > 70.99% 0.01% fio [k] call_rwsem_down_write_failed > 69.43% 1.18% fio [k] rwsem_down_write_failed > 65.51% 54.57% fio [k] osq_lock > 9.72% 7.99% fio [k] __raw_callee_save___kvm_vcpu_is_preempted > 4.16% 4.16% fio [k] __kvm_vcpu_is_preempted > > So making vcpu_is_preempted() a callee-save function has a pretty high > cost associated with it. As vcpu_is_preempted() is called within the > spinlock, mutex and rwsem slowpaths, there isn't much to gain by making > it callee-save. So it is now changed to a normal function call instead. > Numbers for bare metal too please.
