Hi Marc, On Thu, Jan 05, 2017 at 06:11:14PM +0000, Marc Zyngier wrote: > [adding the arm64 maintainers, plus Mark as arch timer maintainer]
Right, sorry, I should have done that already. > > On 10/12/16 20:47, Christoffer Dall wrote: > > Using the physical counter allows KVM to retain the offset between the > > virtual and physical counter as long as it is actively running a VCPU. > > > > As soon as a VCPU is released, another thread is scheduled or we start > > running userspace applications, we reset the offset to 0, so that VDSO > > operations can still read the virtual counter and get the same view of > > time as the kernel. > > > > This opens up potential improvements for KVM performance. > > > > VHE kernels or kernels using the virtual timer are unaffected by this. > > > > Signed-off-by: Christoffer Dall <[email protected]> > > --- > > arch/arm64/include/asm/arch_timer.h | 6 ++++-- > > drivers/clocksource/arm_arch_timer.c | 2 +- > > 2 files changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/arch/arm64/include/asm/arch_timer.h > > b/arch/arm64/include/asm/arch_timer.h > > index eaa5bbe..cec2549 100644 > > --- a/arch/arm64/include/asm/arch_timer.h > > +++ b/arch/arm64/include/asm/arch_timer.h > > @@ -139,11 +139,13 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl) > > > > static inline u64 arch_counter_get_cntpct(void) > > { > > + u64 cval; > > /* > > * AArch64 kernel and user space mandate the use of CNTVCT. > > */ > > - BUG(); > > - return 0; > > + isb(); > > + asm volatile("mrs %0, cntpct_el0" : "=r" (cval)); > > + return cval; > > } > > > > static inline u64 arch_counter_get_cntvct(void) > > diff --git a/drivers/clocksource/arm_arch_timer.c > > b/drivers/clocksource/arm_arch_timer.c > > index 73c487d..a5b0789 100644 > > --- a/drivers/clocksource/arm_arch_timer.c > > +++ b/drivers/clocksource/arm_arch_timer.c > > @@ -597,7 +597,7 @@ static void __init arch_counter_register(unsigned type) > > > > /* Register the CP15 based counter if we have one */ > > if (type & ARCH_CP15_TIMER) { > > - if (IS_ENABLED(CONFIG_ARM64) || arch_timer_uses_ppi == VIRT_PPI) > > + if (arch_timer_uses_ppi == VIRT_PPI || is_kernel_in_hyp_mode()) > > Why do we have this is_kernel_in_hyp_mode clause? I can't think of any > reason for a VHE kernel to use the virtual counter at all... > Good question. I think I just didn't want to change behavior from the existing functionality mre than necessary. Note that on a VHE kernel this will be the EL2 virtual counter, not the EL1 virtual counter, due to the register redirection. Are the virtual and physical EL2 counters always equivalent on a VHE system? > > arch_timer_read_counter = arch_counter_get_cntvct; > > else > > arch_timer_read_counter = arch_counter_get_cntpct; > > > Thanks, -Christoffer _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
