On Wed, 4 Jun 2014, Jon Mason wrote:
On Tue, Jun 03, 2014 at 03:01:31PM -0600, Bjorn Helgaas wrote:
[+cc Yijing, Jon]
The PCI core should be doing something intelligent here. If we can't
configure MPS safely, we should prevent the device from being enabled.
But this is stuff the PCI core doesn't implement yet.
The tuning of the MPS is disabled by default, which is why the warning
is there. Now, we can attempt to tune it regardless of whether tuning
is enabled (assuming this device is the only one under the root port),
we can fail to all the hotplug, or we can enable "safe" tuning by
default. The first option seems a bit hacky. The second will fail
too often, since the MPSS of the hotplugged device would have to match
the MPS setting of slot/fabric. The third seems like the best option.
It's hard to reconfigure MPS after boot because it affects other
devices in the system, and I don't think we can always change the
settings of other devices while they're active.
Unless the slot is under its own root port, otherwise the MPS will
have to be floored. This is the behavior in the "safe" tuning.
I suggest that the "safe" tuning get made the default behavior and we
let it soak for a little while to shake out any issues that there may
be.
Thanks for all the info. I've tried different tunings on several different
platforms that were all failing before. The 'safe' tuning was the only
one successful on all platforms, so just providing a data point that
this appears to be a good direction to go.
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