2017-10-06 22:03+0800, Wanpeng Li: > 2017-10-06 21:03 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: > > 2017-10-06 07:14+0800, Wanpeng Li: > >> 2017-10-06 2:14 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: > >> > 2017-10-05 07:35-0700, Wanpeng Li: > >> >> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > >> >> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now); > >> >> + if (ktime_to_ns(remaining) < 0) > >> >> + remaining = 0; > >> >> + delta = mod_64(ktime_to_ns(remaining), apic->lapic_timer.period); > >> >> + > >> >> + if (!delta) > >> >> + return false; > >> >> + > >> >> + apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT) > >> >> + * APIC_BUS_CYCLE_NS * apic->divide_count; > >> > > >> > I'd prefer to apply the rate limiting (done earlier in this function) to > >> > the period. This version allows the guest to configure 128 times more > >> > frequent interrupts in the host. > >> > (And thinking about it, the version of [2/3] I proposed has similar > >> > problem when switching from one-shot to periodic, only there it is > >> > unpredictably limited by the speed of KVM.) > >> > >> We didn't stop and restart the timer, why the rate will influence us for [2/3]? > > > > It is because of the rate limiting -- the guest could setup a one-shot > > timer with a short expiration and switch to periodic > > Yeah, in addition, I think configure 128 means more slower interrupts > instead of faster. Yes, it says how many cycles it takes to decrement APIC_TMCCT. (I only concerned about the case where rate limit was configured with divide_count=128 and then switched to 1.)
