On Wed, 2018-08-15 at 15:40 -0700, Guenter Roeck wrote: > On Thu, Aug 16, 2018 at 07:50:13AM +1000, Benjamin Herrenschmidt wrote: > > (Resent with lkml on copy) > > > > [Note: This isn't meant to be merged, it need splitting at the very > > least, see below] > > > > This is something I cooked up quickly today to test if that would fix > > my problems with large number of switch and NVME devices on POWER. > > > > Is that a problem that can be reproduced with a qemu setup ? With difficulty... mt-tcg might help, but you need a rather large systems to reproduce it. My repro-case is a 2 socket POWER9 system (about 40 cores off the top of my mind, so 160 threads) with 72 NVME devices underneath a tree of switches (I don't have the system at hand today to check how many). It's possible to observe it I suppose on a smaller system (in theory a single bridge with 2 devices is enough) but in practice the timing is extremely hard to hit. You need a combination of: - The bridges come up disabled (which is the case when Linux does the resource assignment, such as on POWER but not on x86 unless it's hotplug) - The nvme devices try to enable them simultaneously Also the resulting error is a UR, I don't know how well qemu models that. On the above system, I get usually *one* device failing due to the race out of 72, and not on every boot. However, the bug is known (see Bjorn's reply to the other thread) "Re: PCIe enable device races (Was: [PATCH v3] PCI: Data corruption happening due to race condition)" on linux-pci, so I'm not the only one with a repro-case around. Cheers, Ben.
