> -----Original Message----- > From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx] On > Behalf Of Eli Britstein > Sent: Monday, April 11, 2016 2:21 PM > To: kvm@xxxxxxxxxxxxxxx > Subject: IVSHMEM device performance > > 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. Hi Eli, I think you can try the following two things: 1. use ioremap_cache() to map the PCI bar, instead of ioremap(); 2. touch the entire bar memory before using it. Best, Wei -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
