On 5 October 2015 at 15:27, Paolo Bonzini <pbonz...@redhat.com> wrote: > I remember seeing a bug where this terrible implementation caused > divisions by zero on the host. The default implementation in > include/qemu/timer.h should be changed to > qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL). > > Note that in practice this terrible implementation is only used on > ARM/AArch64. Is PMCCNTR or something similar accessible from userspace? > I guess no, since even write access is enabled via PMUSERENR (and in > general PMUSERENR ought to be false on a preemptive-multitasking OS).
Yeah, there's no guarantee on userspace access. I think the fastest way to get some kind of count is to use a library function that boils down to gettimeofday(2), which we will do purely in userspace in the kernel VDSO if possible. thanks -- PMM
