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[Qemu-devel] How to map PCI memory into the VM without trapping

From: Frank Berreth
Subject: [Qemu-devel] How to map PCI memory into the VM without trapping
Date: Mon, 3 May 2010 14:07:42 -0700


I am using a modified patch for the ivshmem device that was posted here recently and discovered some performance issues with it. Essentially I measure write performance into the PCI memory that is mapped into the VM as really slow (about 60mb/sec). I assume that is because there is trapping on each memory access (there are no handlers installed for handling read/write access to that memory though). The device shows up in the guest as a UIO device but I also tried accessing other PCI memory like the vga memory (16mb from vga-pci.c) and it has similar performance (through /sys/device/.../resource...).

My question is how I can map that memory into the VM so it doesn't get trapped on in the normal use case. The mappings (registering PCI bar etc) is done as in the patch submitted recently).


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