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
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/
Thanks,
Kunkun Jiang
Signed-off-by: Keqian Zhu <zhukeqi...@huawei.com>
Signed-off-by: Kunkun Jiang <jiangkun...@huawei.com>
---
migration/ram.c | 39 +++++++++++++++++++--------------------
1 file changed, 19 insertions(+), 20 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index 9fc5b2997c..28215aefe4 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1991,6 +1991,8 @@ static int ram_save_host_page(RAMState *rs,
PageSearchStatus *pss,
int pages = 0;
size_t pagesize_bits =
qemu_ram_pagesize(pss->block) >> TARGET_PAGE_BITS;
+ unsigned long hostpage_boundary =
+ QEMU_ALIGN_UP(pss->page + 1, pagesize_bits);
unsigned long start_page = pss->page;
int res;
@@ -2003,30 +2005,27 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
int pages_this_iteration = 0;
/* Check if the page is dirty and send it if it is */
- if (!migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
- pss->page++;
- continue;
- }
-
- pages_this_iteration = ram_save_target_page(rs, pss, last_stage);
- if (pages_this_iteration < 0) {
- return pages_this_iteration;
- }
+ if (migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
+ pages_this_iteration = ram_save_target_page(rs, pss, last_stage);
+ if (pages_this_iteration < 0) {
+ return pages_this_iteration;
+ }
- pages += pages_this_iteration;
- pss->page++;
- /*
- * Allow rate limiting to happen in the middle of huge pages if
- * something is sent in the current iteration.
- */
- if (pagesize_bits > 1 && pages_this_iteration > 0) {
- migration_rate_limit();
+ pages += pages_this_iteration;
+ /*
+ * Allow rate limiting to happen in the middle of huge pages if
+ * something is sent in the current iteration.
+ */
+ if (pagesize_bits > 1 && pages_this_iteration > 0) {
+ migration_rate_limit();
+ }
}
- } while ((pss->page & (pagesize_bits - 1)) &&
+ pss->page = migration_bitmap_find_dirty(rs, pss->block, pss->page);
+ } while ((pss->page < hostpage_boundary) &&
offset_in_ramblock(pss->block,
((ram_addr_t)pss->page) << TARGET_PAGE_BITS));
- /* The offset we leave with is the last one we looked at */
- pss->page--;
+ /* The offset we leave with is the min boundary of host page and block */
+ pss->page = MIN(pss->page, hostpage_boundary) - 1;
res = ram_save_release_protection(rs, pss, start_page);
return (res < 0 ? res : pages);
--
2.23.0