On Mon, Mar 08, 2021 at 09:58:02PM +0800, Kunkun Jiang wrote: > Hi, > > On 2021/3/5 22:30, Peter Xu wrote: > > On Fri, Mar 05, 2021 at 03:50:35PM +0800, Kunkun Jiang wrote: > > > Starting from pss->page, ram_save_host_page() will check every page > > > and send the dirty pages up to the end of the current host page or > > > the boundary of used_length of the block. If the host page size is > > > a huge page, the step "check" will take a lot of time. > > > > > > This will improve performance to use migration_bitmap_find_dirty(). > > Is there any measurement done? > I tested it on Kunpeng 920. VM params: 1U 4G( page size 1G). > The time of ram_save_host_page() in the last round of ram saving: > before optimize: 9250us after optimize: 34us
Looks like an idle VM, but still this is a great improvement. Would you mind add this into the commit message too? > > This looks like an optimization, but to me it seems to have changed a lot > > context that it doesn't need to... Do you think it'll also work to just > > look up > > dirty again and update pss->page properly if migration_bitmap_clear_dirty() > > returned zero? > > > > Thanks, > This just inverted the body of the loop, suggested by @David Edmondson. > Here is the v2[1]. Do you mean to change it like this? > > [1]: > http://patchwork.ozlabs.org/project/qemu-devel/patch/20210301082132.1107-4-jiangkun...@huawei.com/ I see, then it's okay - But indeed I still prefer your previous version. :) Thanks, -- Peter Xu
