I've tested and applied this patchset on my tree. Currently, vga cards that allocate vga ram, register it as regular ram, and then request dirty logging from kvm (which is required for this hack to function correctly). Both these operations involve memory slot update and flush in kvm and in vhost which is a slow operation.
This was observed to slow down windows guests with a huge amount of memory and cpu and with cirrus vga. As a solution, this adds an explicit flag that will enable dirty logging directly when registering the ram. kvm then needs a single system call to update tables for vga ram, vhost-net can simply ignore it. This patchset only updates the cirrus vga lfb vram mapping. Follow-up patchsets will update all the rest of the cards and then remove vga_dirty_log_xxx completely. This replaces the RFC patchset as well as the RFC 'vga: flag vga ram for notifiers'. Changes since RFC: in patch vhost: optimize out no-change assignment, moved the no-change test to later in function to catch more cases. Test setup: host: 512G -smp 64 guest -m 256G -smp 32 cirrus vga; windows boot time goes down from 30 min to 1 min. Michael S. Tsirkin (5): cpu: add set_memory flag to request dirty logging kvm: halve number of set memory calls for vga vhost: skip memory which needs dirty logging vhost: optimize out no-change assignment cirrus_vga: flag on-device ram for dirty logging cpu-common.h | 22 +++++++++++++++---- exec.c | 14 +++++++----- hw/cirrus_vga.c | 16 +++++++++---- hw/vhost.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++- kvm-all.c | 62 +++++++++++++++++++++++++++++++++--------------------- 5 files changed, 134 insertions(+), 41 deletions(-) -- 1.7.3.2.91.g446ac
