From mboxrd@z Thu Jan 1 00:00:00 1970 From: benh@kernel.crashing.org (Benjamin Herrenschmidt) Date: Sun, 06 Oct 2013 17:19:46 +1100 Subject: [PATCH RFC 00/77] Re-design MSI/MSI-X interrupts enablement pattern In-Reply-To: <20131006060243.GB28142@dhcp-26-207.brq.redhat.com> References: <1380840585.3419.50.camel@bwh-desktop.uk.level5networks.com> <20131004082920.GA4536@dhcp-26-207.brq.redhat.com> <1380922156.3214.49.camel@bwh-desktop.uk.level5networks.com> <20131005142054.GA11270@dhcp-26-207.brq.redhat.com> <1381009586.645.141.camel@pasglop> <20131006060243.GB28142@dhcp-26-207.brq.redhat.com> Message-ID: <1381040386.645.143.camel@pasglop> On Sun, 2013-10-06@08:02 +0200, Alexander Gordeev wrote: > On Sun, Oct 06, 2013@08:46:26AM +1100, Benjamin Herrenschmidt wrote: > > On Sat, 2013-10-05@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. > > > > >