On Fri, Sep 20, 2013 at 07:26:03AM -0500, Tejun Heo wrote: > Hello, > > On Wed, Sep 18, 2013 at 06:50:45PM +0200, Alexander Gordeev wrote: > > Actually, I do not see much contradiction with what I proposed. The > > key words here "determine the number of MSIs the controller wants". > > > > In general case it is not what pci_msix_table_size() returns (or at > > least we should not limit ourselves to it) - there could be non- > > standard means to report number of MSIs: hardcoded, version-dependant, > > device-specific registers etc. > > > > Next, if we opt to determine the number of MSIs by non-MSI standard > > means then there is no reason not to call pci_get_msix_limit() (or > > whatever) at this step. > > Yeah, that's all fine. My point is that we shouldn't try to use > "degraded" multiple MSI mode where the number of MSIs allocated is > smaller than performing full multiple MSI operation. How that number > is determined doesn't really matter but that number is a property > which is solely decided by the device driver, right? If a device > needs full multiple MSI mode, given specific configuration, it needs > >= X number of MSIs and that's the number it should request. Sure, the driver is in full control. If it can ONLY work with N MSIs then it should try for N, else fallback to 1. But some drivers are able to work with a range of values for N, and performance is improved vs using a single MSI. > > Being Captain Obvious here, but it is up to the device driver to handle > > a failure. There could be no such option as single MSI mode after all :) > > I don't think there actually is a mainstream device which can't > fallback to single interrupt. Anyways, the point is the same, let's > please not try to create an interface which encourages complex retry > logic in its users which are likely to involve less traveled and > tested paths in both the driver and firmware. Why support > 1 MSI at all? It just adds complex logic and less travelled paths in the driver and firmware. cheers -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
