Re: [PATCH 1/1] pcie-root-port: Fast PCIe root ports for new machine

[Daniel P . Berrangé]

On Tue, Dec 03, 2024 at 10:58:22AM +0000, Gao,Shiyuan via wrote:
> > Some hardware devices now support PCIe 5.0, so change the default
> > speed of the PCIe root port on new machine types.
> >
> > For passthrough Nvidia H20, this will be able to increase the h2d/d2h
> > bandwidth ~17%.
> >
> > Origin:
> > [CUDA Bandwidth Test] - Starting...
> > Running on...
> >
> > Device 0: NVIDIA H20
> > Quick Mode
> >
> > Host to Device Bandwidth, 1 Device(s)
> > PINNED Memory Transfers
> >    Transfer Size (Bytes)    Bandwidth(MB/s)
> >    33554432            45915.4
> >
> > Device to Host Bandwidth, 1 Device(s)
> > PINNED Memory Transfers
> >    Transfer Size (Bytes)    Bandwidth(MB/s)
> >    33554432            45980.3
> >
> > Device to Device Bandwidth, 1 Device(s)
> > PINNED Memory Transfers
> >    Transfer Size (Bytes)    Bandwidth(MB/s)
> >    33554432            1842886.8
> >
> > Result = PASS
> >
> > With this patch:
> > [CUDA Bandwidth Test] - Starting...
> > Running on...
> >
> > Device 0: NVIDIA H20
> > Quick Mode
> >
> > Host to Device Bandwidth, 1 Device(s)
> > PINNED Memory Transfers
> >    Transfer Size (Bytes)    Bandwidth(MB/s)
> >    33554432                 53682.0
> >
> > Device to Host Bandwidth, 1 Device(s)
> > PINNED Memory Transfers
> >    Transfer Size (Bytes)    Bandwidth(MB/s)
> >    33554432                 53766.0
> >
> > Device to Device Bandwidth, 1 Device(s)
> > PINNED Memory Transfers
> >    Transfer Size (Bytes)    Bandwidth(MB/s)
> >    33554432                 1842555.1
> >
> > Result = PASS
> >
> > Signed-off-by: Gao Shiyuan <gaoshiyuan@baidu.com>
> > ---
> > hw/core/machine.c                  | 1 +
> > hw/pci-bridge/gen_pcie_root_port.c | 2 +-
> > 2 files changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index a35c4a8fae..afef55626d 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -38,6 +38,7 @@
> >
> > GlobalProperty hw_compat_9_1[] = {
> >      { TYPE_PCI_DEVICE, "x-pcie-ext-tag", "false" },
> > +    { "pcie-root-port", "x-speed", "16" },
> > };
> > const size_t hw_compat_9_1_len = G_N_ELEMENTS(hw_compat_9_1);
> >
> > diff --git a/hw/pci-bridge/gen_pcie_root_port.c 
> > b/hw/pci-bridge/gen_pcie_root_port.c
> > index 784507c826..c24ce1f2d1 100644
> > --- a/hw/pci-bridge/gen_pcie_root_port.c
> > +++ b/hw/pci-bridge/gen_pcie_root_port.c
> > @@ -142,7 +142,7 @@ static Property gen_rp_props[] = {
> >      DEFINE_PROP_SIZE("pref64-reserve", GenPCIERootPort,
> >                       res_reserve.mem_pref_64, -1),
> >      DEFINE_PROP_PCIE_LINK_SPEED("x-speed", PCIESlot,
> > -                                speed, PCIE_LINK_SPEED_16),
> > +                                speed, PCIE_LINK_SPEED_32),
> >      DEFINE_PROP_PCIE_LINK_WIDTH("x-width", PCIESlot,
> >                                  width, PCIE_LINK_WIDTH_32),
> >      DEFINE_PROP_END_OF_LIST()
> > --
> > 2.34.1
> 
> Ping.

There was a question from Jonathan Cameron on the original posting of this
patch that is awaiting your answer....

Regardless, at this time in the release cycle its too late for 9.2, so this
patch would likely need to be adapted for the 10.0 release and to use the
hw_compat_9_2 that will then be added.

With regards,
Daniel
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