On 02/08/2017 02:05 PM, Peter Zijlstra wrote: > 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. I will run the test on bare metal, but I doubt there will be noticeable difference. Cheers, Longman
