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[Qemu-devel] [PATCHv5 10/10] migration: use XBZRLE only after bulk stage
From: |
Peter Lieven |
Subject: |
[Qemu-devel] [PATCHv5 10/10] migration: use XBZRLE only after bulk stage |
Date: |
Tue, 26 Mar 2013 10:58:39 +0100 |
at the beginning of migration all pages are marked dirty and
in the first round a bulk migration of all pages is performed.
currently all these pages are copied to the page cache regardless
of whether they are frequently updated or not. this doesn't make sense
since most of these pages are never transferred again.
this patch changes the XBZRLE transfer to only be used after
the bulk stage has been completed. that means a page is added
to the page cache the second time it is transferred and XBZRLE
can benefit from the third time of transfer.
since the page cache is likely smaller than the number of pages
it's also likely that in the second round the page is missing in the
cache due to collisions in the bulk phase.
on the other hand a lot of unnecessary mallocs, memdups and frees
are saved.
the following results have been taken earlier while executing
the test program from docs/xbzrle.txt. (+) with the patch and (-)
without. (thanks to Eric Blake for reformatting and comments)
+ total time: 22185 milliseconds
- total time: 22410 milliseconds
Shaved 0.3 seconds, better than 1%!
+ downtime: 29 milliseconds
- downtime: 21 milliseconds
Not sure why downtime seemed worse, but probably not the end of the world.
+ transferred ram: 706034 kbytes
- transferred ram: 721318 kbytes
Fewer bytes sent - good.
+ remaining ram: 0 kbytes
- remaining ram: 0 kbytes
+ total ram: 1057216 kbytes
- total ram: 1057216 kbytes
+ duplicate: 108556 pages
- duplicate: 105553 pages
+ normal: 175146 pages
- normal: 179589 pages
+ normal bytes: 700584 kbytes
- normal bytes: 718356 kbytes
Fewer normal bytes...
+ cache size: 67108864 bytes
- cache size: 67108864 bytes
+ xbzrle transferred: 3127 kbytes
- xbzrle transferred: 630 kbytes
...and more compressed pages sent - good.
+ xbzrle pages: 117811 pages
- xbzrle pages: 21527 pages
+ xbzrle cache miss: 18750
- xbzrle cache miss: 179589
And very good improvement on the cache miss rate.
+ xbzrle overflow : 0
- xbzrle overflow : 0
Signed-off-by: Peter Lieven <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
Reviewed-by: Orit Wasserman <address@hidden>
---
arch_init.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch_init.c b/arch_init.c
index a522735..e1af898 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -466,7 +466,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
acct_info.skipped_pages++;
bytes_sent = 0;
}
- } else if (migrate_use_xbzrle()) {
+ } else if (!ram_bulk_stage && migrate_use_xbzrle()) {
current_addr = block->offset + offset;
bytes_sent = save_xbzrle_page(f, p, current_addr, block,
offset, cont, last_stage);
--
1.7.9.5
- [Qemu-devel] [PATCHv5 00/10] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 04/10] buffer_is_zero: use vector optimizations if possible, Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 05/10] bitops: unroll while loop in find_next_bit(), Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 08/10] migration: do not sent zero pages in bulk stage, Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 09/10] migration: do not search dirty pages in bulk stage, Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 07/10] migration: add an indicator for bulk state of ram migration, Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 06/10] migration: search for zero instead of dup pages, Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 10/10] migration: use XBZRLE only after bulk stage,
Peter Lieven <=
- [Qemu-devel] [PATCHv5 01/10] move vector definitions to qemu-common.h, Peter Lieven, 2013/03/26
- [Qemu-devel] [PATCHv5 02/10] add a zero splat vector to qemu-common.h, Peter Lieven, 2013/03/26
[Qemu-devel] [PATCHv5 03/10] cutils: add a function to find non-zero content in a buffer, Peter Lieven, 2013/03/26