On Thu, Sep 26, 2013 at 04:39:02PM +0200, Alexander Gordeev wrote: > On Thu, Sep 26, 2013 at 09:11:47AM -0400, Tejun Heo wrote: > > > Because otherwise we will re-introduce a problem described by Michael: > > > "We have a small number of MSIs available, limited by hardware & > > > firmware, if we don't impose a quota then the first device that probes > > > will get most/all of the MSIs and other devices miss out." > > > > Still not following. Why wouldn't just letting the drivers request > > the optimal number they want and falling back to single interrupt mode > > work? ie. why can't we just have an all or nothing interface? > > I can imagine a scenario where the first device probes in, requests its > optimal number, acquires that number and exhausts MSIs in pSeries firmware. > The next few devices possibly end up with single MSI, since no MSIs left > to satisfy their optimal numbers. If one of those single-MSI'ed devices > happened to be a high-performance HBA hitting a degraded performance that > alone would force (IBM) to introduce the quotas. Yes that's exactly the scenario, and I didn't imagine it, our test people actually hit it and yelled at me. I don't remember exactly which adapters it was, I might be able to find the details if I looked hard, a quick search through my mail archive didn't find it - it might have come in via irc / bugzilla etc. cheers -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
