On Sun, Oct 06, 2013 at 05:19:46PM +1100, Benjamin Herrenschmidt wrote:

On Sun, 2013-10-06 at 08:02 +0200, Alexander Gordeev wrote:

quoted

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.

There is one major flaw in min-max approach - the generic MSI layer
will have to take decisions on exact number of MSIs to request, not
device drivers.

This will never work for all devices, because there might be specific
requirements which are not covered by the min-max. That is what Ben
described "...say, any even number within a certain range". Ben suggests
to leave the existing loop scheme to cover such devices, which I think is
not right.

What about introducing pci_lock_msi() and pci_unlock_msi() and let device
drivers care about their ranges and specifics in race-safe manner?
I do not call to introduce it right now (since it appears pSeries has not
been hitting the race for years) just as a possible alternative to Ben's
proposal.

-- 
Regards,
Alexander Gordeev
agordeev@redhat.com