On Sun, 2013-10-06 at 08:02 +0200, Alexander Gordeev wrote: > On Sun, Oct 06, 2013 at 08:46:26AM +1100, Benjamin Herrenschmidt wrote: > > On Sat, 2013-10-05 at 16:20 +0200, Alexander Gordeev wrote: > > > So my point is - drivers should first obtain a number of MSIs they *can* > > > get, then *derive* a number of MSIs the device is fine with and only then > > > request that number. Not terribly different from memory or any other type > > > of resource allocation ;) > > > > What if the limit is for a group of devices ? Your interface is racy in > > that case, another driver could have eaten into the limit in between the > > calls. > > Well, the another driver has had a better karma ;) But seriously, the > current scheme with a loop is not race-safe wrt to any other type of > resource which might exhaust. What makes the quota so special so we > should care about it and should not care i.e. about lack of msi_desc's? I'm not saying the current scheme is better but I prefer the option of passing a min,max to the request function. > Yeah, I know the quota might hit more likely. But why it is not addressed > right now then? Not a single function in chains... > rtas_msi_check_device() -> msi_quota_for_device() -> traverse_pci_devices() > rtas_setup_msi_irqs() -> msi_quota_for_device() -> traverse_pci_devices() > ...is race-safe. So if it has not been bothering anyone until now then > no reason to start worrying now :) > > In fact, in the current design to address the quota race decently the > drivers would have to protect the *loop* to prevent the quota change > between a pci_enable_msix() returned a positive number and the the next > call to pci_enable_msix() with that number. Is it doable? I am not advocating for the current design, simply saying that your proposal doesn't address this issue while Ben's does. Cheers, Ben. > > Ben. > > > > >
