On Tue, Jan 14, 2014 at 3:54 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> [+cc Jon, Yijing]
>
> On Thu, Jan 9, 2014 at 5:46 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
>> looks like we have some problem with MPSS.
>>
>> +-02.2-[10-1f]----00.0-[11-13]--+-02.0-[12]--+-00.0
>> | | \-00.1
>> | \-03.0-[13]----00.0
>>
>> kernel boot with pce_bus_perf:
>> 00:02.2: cap/ctl: 256/256
>> 10:00.0: cap/ctl: 256/256
>> 11:02.0: cap/ctl: 256/256
>> 12:00.0: cap/ctl: 128/128
>> 12:00.1: cap/ctl: 128/128
>>
>> 11:03.0: cap/ctl: 256/256
>> 13:00.0: cap/ctl: 256/256
>>
>> Should we set MPSS to 128?
>
> Please propose a patch and/or open a bug report. I don't do enough
> with MPS to make the problem and its solution immediately obvious to
> me.
Not a lot of verbiage in here, but I believe this is the expected
behavior for the "pcie_bus_perf" kernel boot parm. With it, each pci
device sets its MPS to the max of the parent
>From the commit log:
- A more optimal way is possible, if it falls within a couple of
constraints:
* The top-level host bridge will never generate packets larger than the
smallest TLP (or if it can be controlled independently from its MPS at
least)
* The device will never generate packets larger than MPS (which can be
configured via MRRS)
* No support of direct PCI-E <-> PCI-E transfers between devices without
some additional code to specifically deal with that case
Then we can use an approach that basically ignores downstream requests
and focuses exclusively on upstream requests. In that case, all we need
to care about is that a device MPS is no larger than its parent MPS,
which allows us to keep all switches/bridges to the max MPS supported by
their parent and eventually the PHB.
If this is not behaving as described (which I can't tell from the log
above), then feel free to assign the bug to me.
Thanks,
Jon
>
> Bjorn
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
