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[PATCH v4 2/2] migration/ram: Optimize ram_save_host_page()
From: |
Kunkun Jiang |
Subject: |
[PATCH v4 2/2] migration/ram: Optimize ram_save_host_page() |
Date: |
Tue, 16 Mar 2021 20:57:16 +0800 |
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.
It will improve performance to use migration_bitmap_find_dirty().
Tested on Kunpeng 920; VM parameters: 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
Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
---
migration/ram.c | 39 +++++++++++++++++++--------------------
1 file changed, 19 insertions(+), 20 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index 3eb5b0d7a7..1d9c24aa85 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1993,6 +1993,8 @@ static int ram_save_host_page(RAMState *rs,
PageSearchStatus *pss,
int tmppages, 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,
do {
/* Check the pages is dirty and if it is send it */
- if (!migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
- pss->page++;
- continue;
- }
-
- tmppages = ram_save_target_page(rs, pss, last_stage);
- if (tmppages < 0) {
- return tmppages;
- }
+ if (migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
+ tmppages = ram_save_target_page(rs, pss, last_stage);
+ if (tmppages < 0) {
+ return tmppages;
+ }
- pages += tmppages;
- 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 && tmppages > 0) {
- migration_rate_limit();
+ pages += tmppages;
+ /*
+ * Allow rate limiting to happen in the middle of huge pages if
+ * something is sent in the current iteration.
+ */
+ if (pagesize_bits > 1 && tmppages > 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