migration/ram: Optimize ram_save_host_page()
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> Reviewed-by: Peter Xu <peterx@redhat.com> Message-Id: <20210316125716.1243-3-jiangkunkun@huawei.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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@ -2013,6 +2013,8 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
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int tmppages, pages = 0;
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size_t pagesize_bits =
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qemu_ram_pagesize(pss->block) >> TARGET_PAGE_BITS;
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unsigned long hostpage_boundary =
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QEMU_ALIGN_UP(pss->page + 1, pagesize_bits);
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unsigned long start_page = pss->page;
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int res;
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@ -2023,18 +2025,13 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
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do {
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/* Check the pages is dirty and if it is send it */
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if (!migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
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pss->page++;
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continue;
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}
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if (migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
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tmppages = ram_save_target_page(rs, pss, last_stage);
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if (tmppages < 0) {
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return tmppages;
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}
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pages += tmppages;
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pss->page++;
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/*
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* Allow rate limiting to happen in the middle of huge pages if
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* something is sent in the current iteration.
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@ -2042,11 +2039,13 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
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if (pagesize_bits > 1 && tmppages > 0) {
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migration_rate_limit();
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}
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} while ((pss->page & (pagesize_bits - 1)) &&
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}
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pss->page = migration_bitmap_find_dirty(rs, pss->block, pss->page);
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} while ((pss->page < hostpage_boundary) &&
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offset_in_ramblock(pss->block,
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((ram_addr_t)pss->page) << TARGET_PAGE_BITS));
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/* The offset we leave with is the last one we looked at */
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pss->page--;
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/* The offset we leave with is the min boundary of host page and block */
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pss->page = MIN(pss->page, hostpage_boundary) - 1;
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res = ram_save_release_protection(rs, pss, start_page);
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return (res < 0 ? res : pages);
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