Re: IVSHMEM device performance

[Markus Armbruster <armbru@redhat.com>]

Cc: qemu-devel

Eli Britstein <eli.britstein@toganetworks.com> 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.