[ovs-discuss] IVSHMEM device performance

[Kavanagh, Mark B]

Hi Eli,

I'm curious as to why you want to use IVSHMEM devices in a setup like this - the whole point of IVSHMEM devices is that the same memory is shared between host and guest, such that mbufs can be passed directly between rings 'zero-copy', thus side-stepping the performance penalties inherent in memcpy.

Perhaps a vhost-user device would better suit your needs?

Thanks,
Mark

>-----Original Message-----
>From: discuss [mailto:discuss-bounces at openvswitch.org] On Behalf Of Eli Britstein
>Sent: Wednesday, March 30, 2016 3:02 PM
>To: discuss at openvswitch.org
>Subject: [ovs-discuss] IVSHMEM device performance
>
>Hi
>
>In a VM, I add a IVSHMEM device, on which the MBUFS mempool resides, and also rings I create.
>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 (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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