Il mar 19 nov 2024, 22:43 Peter Xu <pet...@redhat.com> ha scritto: > > The easiest way to check is probably to print the type of every > successful > > object_dynamic_cast and object_class_dynamic_cast. I suspect the result > > will be virtio-blk-device and/or scsi-hd, but maybe those already do an > > unsafe cast (pointer type cast) instead of object_dynamic_cast. > > Yes, it sounds more reasonable to me to optimize specific call sites so far > rather than provides something generic.
Though it could still be a > generic API so that devices can opt-in. One of the things that I am excited about for Rust is checking at compile time whether a cast is to a superclass, which makes it safe automatically. > I can give it some measurement if there is, otherwise I'm > > > guessing whatever changes could fall into the noise. > > > > > > Yes, probably. At most you can identify if there any heavy places out of > > the 34000 calls, and see if they can use an unsafe cast. > > I can still trivially do this. > > I traced qemu using bpf Nice! I want to know more. :)) A > and interestingly in my case close to half (over > 10000+) of the calls are about ahci_irq_lower() from different higher level > stack (yeah I used IDE in my setup.. with a split irqchi..), where it has: > > PCIDevice *pci_dev = (PCIDevice *) > object_dynamic_cast(OBJECT(dev_state), > > TYPE_PCI_DEVICE); > > So IIUC that can be open to a unsafe cast too Hmm no it can't because there's also sysbus AHCI. The fix would be to add an AHCIClass and make irq toggling into a method there but considering IDE is ODD FIXES stage, I'm not sure if I should send a > patch at all. However I copied John regardless. > Well, MAINTAINERS only says the kind of work that the maintainer is doing, you can always do more. However it seems like not a small amount, so maybe adding a comment is enough if somebody else wants to do it? Paolo > Thanks, > > -- > Peter Xu > >
