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Re: [Qemu-devel] [PATCH] Revert "memory: syncronize kvm bitmap using bit


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] Revert "memory: syncronize kvm bitmap using bitmaps operations"
Date: Wed, 29 Jan 2014 11:03:36 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0

Il 29/01/2014 09:12, Alexey Kardashevskiy ha scritto:
On 01/29/2014 06:30 PM, Paolo Bonzini wrote:
Il 29/01/2014 06:50, Alexey Kardashevskiy ha scritto:
Since 64K system page size is quite popular configuration on PPC64,
the original patch breaks migration.

Signed-off-by: Alexey Kardashevskiy <address@hidden>
---
 include/exec/ram_addr.h | 54
+++++++++++++++++--------------------------------
 1 file changed, 18 insertions(+), 36 deletions(-)

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 33c8acc..c6736ed 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -83,47 +83,29 @@ static inline void
cpu_physical_memory_set_dirty_lebitmap(unsigned long *bitmap,
                                                           ram_addr_t start,
                                                           ram_addr_t pages)
 {
-    unsigned long i, j;
+    unsigned int i, j;
     unsigned long page_number, c;
     hwaddr addr;
     ram_addr_t ram_addr;
-    unsigned long len = (pages + HOST_LONG_BITS - 1) / HOST_LONG_BITS;
+    unsigned int len = (pages + HOST_LONG_BITS - 1) / HOST_LONG_BITS;
     unsigned long hpratio = getpagesize() / TARGET_PAGE_SIZE;
-    unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);

-    /* start address is aligned at the start of a word? */
-    if (((page * BITS_PER_LONG) << TARGET_PAGE_BITS) == start) {

Why not just add " && hpratio == 1" here?

Or fix dirty map to make it 1 bit per system page size (may be the fix is
coming, who knows, but I am just not ready to do this now). Or do tricks
with bits and support hpratio!=1. I could not choose and decided to revert
it for now :)

Can you post the patch that adds " && hpratio == 1"?

Do we really earn a lot here?

Yes, because this is the only part of migration that runs with the iothread lock taken. Without Juan's patches you can see large guests hiccups that last a few seconds.

Paolo



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