On Sun, Mar 28, 2021 at 12:04:35AM +0100, Heiner Kallweit wrote: > On 26.03.2021 22:26, Bjorn Helgaas wrote: > > [+cc Randy, Andrew (though I'm sure you have zero interest in this > > ancient question :))] > > > > On Wed, Dec 09, 2020 at 09:31:21AM +0100, Heiner Kallweit wrote: > >> pci_set_mwi() and pci_try_set_mwi() do exactly the same, just that the > >> former one is declared as __must_check. However also some callers of > >> pci_set_mwi() have a comment that it's an optional feature. I don't > >> think there's much sense in this separation and the use of > >> __must_check. Therefore remove pci_try_set_mwi() and remove the > >> __must_check attribute from pci_set_mwi(). > >> I don't expect either function to be used in new code anyway. > > > > There's not much I like better than removing things. But some > > significant thought went into adding pci_try_set_mwi() in the first > > place, so I need a little more convincing about why it's safe to > > remove it. > > > > Thanks for the link to the 13 yrs old discussion. Unfortunately it > doesn't mention any real argument for the __must_check, just: > > "And one of the reasons for adding the __must_check annotation is to > weed out design errors." > And the very next response in the discussion calls this a "non-argument". > Plus not mentioning what the other reasons could be. I think you're referring to Alan's response [1]: akpm> And we *need* to be excessively anal in the PCI setup code. akpm> We have metric shitloads of bugs due to problems in that area, akpm> and the more formality and error handling and error reporting akpm> we can get in there the better off we will be. ac> No argument there So Alan is actually *agreeing* that "we need to be excessively anal in the PCI setup code," not saying that "weeding out design errors is not an argument for __must_check." > Currently we have three ancient drivers that bail out if the call fails. > Most callers of pci_set_mwi() use the return code only to emit an > error message, but they proceed normally. Majority of users calls > pci_try_set_mwi(). And as stated in the commit message I don't expect > any new usage of pci_set_mwi(). I would love to merge this patch. We just need to clarify the commit log. Right now the only justification is "I don't think there's much sense in the __must_check annotation," which may well be true but could use some support. If MWI is purely an optimization and there's never a functional problem if pci_set_mwi() fails, we should say that (and maybe update any drivers that bail out on failure). Andrew and Alan both seem to agree that MSI *is* purely advisory: akpm> pci_set_mwi() is an advisory thing, and on certain platforms akpm> it might fail to set the cacheline size to the desired number. akpm> This is not a fatal error and the driver can successfully run akpm> at a lesser performance level. ac> Correct. But even after that, Andrew proposed adding pci_try_set_mwi(). So it makes sense to really understand what was going on there so we don't break something in the name of cleaning it up. [1] https://lore.kernel.org/linux-ide/20070405211609.5263d627@xxxxxxxxxxxxxxxxx/ > > The argument should cite the discussion about adding it. I think one > > of the earliest conversations is here: > > https://lore.kernel.org/linux-ide/20070404213704.224128ec.randy.dunlap@xxxxxxxxxx/
