September 5, 2025 at 1:38 PM, "BALATON Zoltan" wrote: > On Thu, 4 Sep 2025, Julian Ganz wrote: > > Even with the existing interfaces, it is more or less possible to > > discern these situations, e.g. as done by the cflow plugin. However, > > this process poses a considerable overhead to the core analysis one may > > intend to perform. > > > I'd rather have overhead in the plugin than in interrupt and exception > handling on every target unless this can be completely disabled > somehow when not needed to not pose any overhead on interrupt handling > in the guest.
The "more or less" is rather heavy here: with the current API there is no way to distinguish between interrupts and exceptions. Double-traps can probably only be detected if you don't rely on weird, very error prone heuristics around TB translations. And as Alex Benée pointed out, qemu can be easily built with plugins disabled. > Have you done any testing on how much overhead this adds > to interrupt heavy guest workloads? At least for PPC these are already > much slower than real CPU so I'd like it to get faster not slower. No, I have not made any performance measurements. However, given that for every single TB execution a similar hook is called already, the impact related to other existing plugin infrastructure _should_ be neglectible. That is, if your workload actually runs any code and is not constantly bombarded with interrupts that _do_ result in a trap (which _may_ happen during some tests). So if you are performance sensitive enough to care, you will very likely want to disable plugins anyway. Regards, Julian
