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. Regards, Wanpeng Li > > It is mostly theoretical as the expiration would have to be long enough > so that the timer doesn't fire before KVM emulates the next instruction > that switches the timer to periodic mode, but shorter than rate limit. > > I see you handled that in v6, thanks!
