Bug 27984 - Batch BAR sizing operations
Summary: Batch BAR sizing operations
Status: NEW
Alias: None
Product: ANCK 6.6 Dev
Classification: ANCK
Component: virt (show other bugs) virt
Version: unspecified
Hardware: All Linux
: P3-Medium S3-normal
Target Milestone: ---
Assignee: maqiao
QA Contact: shuming
URL:
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Keywords:
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Reported: 2025-12-11 09:33 UTC by nizhiguang
Modified: 2025-12-11 09:41 UTC (History)
2 users (show)

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Description nizhiguang hygon_group 2025-12-11 09:33:01 UTC 
在外设直通虚拟机的环境中，PCI驱动会配置外设的Config space, 导致qemu中对外设的bar进行unmap和map操作，对于具有较大bar的设备，比如GPU设备，这种操作将会比较耗时，当直通多个GPU到虚拟机，情况变得更加糟糕。

在qemu的vfio_dma_map和vfio_dma_unmap中添加日志，可以观察到频繁unmap/map GPU的bar。
这个patch将多个配置PCI config space的操作合并，减少Qemu unmap/map GPU bar的操作，对于启动加速效果明显。

测试方法：
1. 不直通GPU到虚拟机，启动时间很短，大约1分钟
2. 直通1个GPU卡到虚拟机，启动时间变长，大约2分钟
3. 直通8张GPU卡到虚拟机，大约15分钟
Comment 1 小龙 admin 2025-12-11 09:41:09 UTC 
The PR Link: https://gitee.com/anolis/cloud-kernel/pulls/6185