[Xen-devel] question: xen/qemu - mmio mapping issues for device pass-through

["Xuquan (Quan Xu)" <xuquan8@xxxxxxxxxx>]

Hello,

I try to pass-through a device with 8G large bar, such as nvidia M60(note1, 
pci-e info as below). It takes about '__15 sconds__' to update 8G large bar in 
QEMU::xen_pt_region_update()..
Specifically, it is xc_domain_memory_mapping() in xen_pt_region_update().

Digged into xc_domain_memory_mapping(), I find it mainly call "do_domctl （…case 
XEN_DOMCTL_memory_mapping…）" 
to mapping mmio region.. of cause, I find out that this mapping could take a 
while in the code comment below ' case XEN_DOMCTL_memory_mapping '.

my questions:
1. could we make this mapping mmio region quicker?
2. if could not, does it limit by hardware performance?



-------------
Note1:
lspci -v -s 86:00.0  (nvidia M60)
86:00.0 3D controller: NVIDIA Corporation Device 13f2 (rev a1)
        Subsystem: NVIDIA Corporation Device 115e
        Flags: bus master, fast devsel, latency 0, IRQ 7
        Memory at c8000000 (32-bit, non-prefetchable) [size=16M]
        Memory at 3f800000000 (64-bit, prefetchable) [size=8G]
        Memory at 3fa00000000 (64-bit, prefetchable) [size=32M]
        Capabilities: [60] Power Management version 3
        Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
        Capabilities: [78] Express Endpoint, MSI 00
        Capabilities: [100] Virtual Channel
        Capabilities: [250] Latency Tolerance Reporting
        Capabilities: [258] #1e
        Capabilities: [128] Power Budgeting <?>
        Capabilities: [420] Advanced Error Reporting
        Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 
<?>
        Capabilities: [900] #19
        Kernel modules: nvidiafb


Thanks!!
-Quan
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