On Thu, Sep 28, 2017 at 06:35:08PM -0300, Marcelo Tosatti wrote: > On Thu, Sep 28, 2017 at 09:22:02AM +0200, Paolo Bonzini wrote: > > On 28/09/2017 02:44, Marcelo Tosatti wrote: > > >> Again: if you have many interruptions, it's not a flaw in KVM or QEMU's > > >> design, it's just that someone is doing something stupid. It could be > > >> the guest (e.g. unnecessary devices or daemons as in the example above), > > >> QEMU (e.g. the RTC emulation used to trigger QEMU timers twice a second > > >> just to increment the clock), or the management (e.g. polling "is the VM > > >> running" 50 times per second). But it can and must be fixed. > > > > > > No, i mean you can run anything in VCPU-0 (it is valid to do that). > > > And that "anything" can generate 1 interrupt per second, 1000 or 10.000 > > > interrupts per second. Which are all valid things to be done. > > > > > > "I can't run a kernel compilation on VCPU-0 because that will impact > > > latency on the realtime VCPU-1" is not acceptable. > > > > That shouldn't happen. Sources of frequent interruptions have all been > > fixed or moved outside the main thread. > > > > If there are more left, report the bug and we'll see how to fix it in > > userspace. > > > > Paolo > > What should not happen? The generation of 10.000 interrupts per second > (say disk IO completion) on a given workload ? Are you suggesting that, workloads in vcpu-0 should be limited in the number of interrupts (and durations of each interruption), so that the realtime vcpu-1's latency requirement is met ? I don't see how that suggestion can work because even if you make each exit small, the frequency of them will cause a latency violation on vcpu-1.
