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[Qemu-devel] [RFC][PATCH 6/9] migration: use XBZRLE only after bulk stag


From: Peter Lieven
Subject: [Qemu-devel] [RFC][PATCH 6/9] migration: use XBZRLE only after bulk stage
Date: Tue, 12 Mar 2013 16:51:58 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130221 Thunderbird/17.0.3

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
if there 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
its 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 unneccssary mallocs, memdups and frees
are saved.

Signed-off-by: Peter Lieven <address@hidden>
---
 arch_init.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch_init.c b/arch_init.c
index 3d09327..04c82e4 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -451,7 +451,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
                                             RAM_SAVE_FLAG_COMPRESS);
                 qemu_put_byte(f, *p);
                 bytes_sent += 1;
-            } 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





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