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SubjectRe: [PATCH v3] PCI: Document PCIE BUS MPS parameters
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On Mon, Jan 28, 2013 at 11:09 PM, Yijing Wang <wangyijing@huawei.com> wrote:
> On 2013/1/29 13:00, Jon Mason wrote:
>> On Fri, Jan 25, 2013 at 2:36 AM, Yijing Wang <wangyijing@huawei.com> wrote:
>>> v0->v1: Update MPS parameters as non-arch and add MRRS
>>> description into pcie_bus_perf parameter suggested
>>> by Andrew Murray.
>>> v1->v2: Update some semantic problems and add MPS and MRRS
>>> explanation suggested by Joe Lawrence and Randy Dunlap.
>>> v2->v3: Update some semantic problems and the description
>>> of pcie_bus_safe and pcie_bus_peer2peer suggested
>>> by Bjorn Helgaas.
>>>
>>> Document PCIE BUS MPS parameters pcie_bus_tune_off, pcie_bus_safe,
>>> pcie_bus_peer2peer, pcie_bus_perf into Documentation/kernel-parameters.txt.
>>> These parameters were introduced by Jon Mason <mason@myri.com> at
>>> commit 5f39e6705 and commit b03e7495a8.
>>>
>>> Signed-off-by: Yijing Wang <wangyijing@huawei.com>
>>> ---
>>> Documentation/kernel-parameters.txt | 13 +++++++++++++
>>> 1 files changed, 13 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>>> index 363e348..2997df2 100644
>>> --- a/Documentation/kernel-parameters.txt
>>> +++ b/Documentation/kernel-parameters.txt
>>> @@ -2227,6 +2227,19 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>> This sorting is done to get a device
>>> order compatible with older (<= 2.4) kernels.
>>> nobfsort Don't sort PCI devices into breadth-first order.
>>> + pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
>>> + tuning and use the BIOS-configured MPS defaults.
>>> + pcie_bus_safe Use the smallest supported MPS of any device
>>> + below a root complex.
>>
>> This isn't correct. It should be something like "The largest MPS
>> common to all devices below the root complex".
>
> Hi Jon,
> Thanks for your review and comment!
> What about "Set every device's MPS to the largest MPSS (Max Payload Size Support)
> common to all devices below the root complex" ?

Sounds great! Thanks so much for documenting this.

>
>>
>>> + pcie_bus_perf Configure device MPS to the largest
>>> + allowable MPS based on its parent bus. Also set
>>> + MRRS (Max Read Request Size) to the largest supported
>>> + value (no larger than the MPS that the device or bus
>>> + can support) for best performance.
>>> + pcie_bus_peer2peer Set every device's MPS to 128B, which
>>> + every device is guaranteed to support. This
>>> + configuration allows peer-to-peer DMA between any pair
>>> + of devices possibly at the cost of reduced performance.
>>> cbiosize=nn[KMG] The fixed amount of bus space which is
>>> reserved for the CardBus bridge's IO window.
>>> The default value is 256 bytes.
>>> --
>>> 1.7.1
>>>
>>>
>>
>> .
>>
>
>
> --
> Thanks!
> Yijing
>


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