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Re: [Qemu-devel] IVSHMEM device performance

From: Markus Armbruster
Subject: Re: [Qemu-devel] IVSHMEM device performance
Date: Mon, 11 Apr 2016 10:56:54 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Cc: qemu-devel

Eli Britstein <address@hidden> writes:

> Hi
> In a VM, I add a IVSHMEM device, on which the MBUFS mempool resides, and also 
> rings I create (I run a DPDK application in the VM).
> I saw there is a performance penalty if I use such device, instead of 
> hugepages (the VM's hugepages). My VM's memory is *NOT* backed with host's 
> hugepages.
> The memory behind the IVSHMEM device is a host hugepage (I use a patched 
> version of QEMU, as provided by Intel).
> I thought maybe the reason is that this memory is seen by the VM as a mapped 
> PCI memory region, so it is not cached, but I am not sure.
> So, my direction was to change the kernel (in the VM) so it will consider 
> this memory as a regular memory (and thus cached), instead of a PCI memory 
> region.
> However, I am not sure my direction is correct, and even if so, I am not sure 
> how/where to change the kernel (my starting point was  mm/mmap.c, but I'm not 
> sure it's the correct place to start).
> Any suggestion is welcomed.
> Thanks,
> Eli.

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