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Re: [PATCH v3 3/3] migration/ram: Optimize ram_save_host_page()
From: |
Peter Xu |
Subject: |
Re: [PATCH v3 3/3] migration/ram: Optimize ram_save_host_page() |
Date: |
Fri, 5 Mar 2021 09:30:33 -0500 |
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?
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,
>
> 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 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
>
--
Peter Xu
- Re: [PATCH v3 1/3] migration/ram: Modify the code comment of ram_save_host_page(), (continued)
[PATCH v3 2/3] migration/ram: Reduce unnecessary rate limiting, Kunkun Jiang, 2021/03/05
- Re: [PATCH v3 2/3] migration/ram: Reduce unnecessary rate limiting, Peter Xu, 2021/03/05
- Re: [PATCH v3 2/3] migration/ram: Reduce unnecessary rate limiting, Kunkun Jiang, 2021/03/08
- Re: [PATCH v3 2/3] migration/ram: Reduce unnecessary rate limiting, Peter Xu, 2021/03/08
- Re: [PATCH v3 2/3] migration/ram: Reduce unnecessary rate limiting, Kunkun Jiang, 2021/03/09
- Re: [PATCH v3 2/3] migration/ram: Reduce unnecessary rate limiting, Peter Xu, 2021/03/09
- Re: [PATCH v3 2/3] migration/ram: Reduce unnecessary rate limiting, Kunkun Jiang, 2021/03/09
[PATCH v3 3/3] migration/ram: Optimize ram_save_host_page(), Kunkun Jiang, 2021/03/05
- Re: [PATCH v3 3/3] migration/ram: Optimize ram_save_host_page(),
Peter Xu <=