Re: [Qemu-devel] [PATCHv5 06/10] migration: search for zero instead of dup pages

[Peter Lieven]

Am 05.04.2013 um 21:23 schrieb Kevin Wolf <address@hidden>:

> Am 26.03.2013 um 10:58 hat Peter Lieven geschrieben:
>> virtually all dup pages are zero pages. remove
>> the special is_dup_page() function and use the
>> optimized buffer_find_nonzero_offset() function
>> instead.
>> 
>> here buffer_find_nonzero_offset() is used directly
>> to avoid the unnecssary additional checks in
>> buffer_is_zero().
>> 
>> raw performace gain checking 1 GByte zeroed memory
>> over is_dup_page() is approx. 10-12% with SSE2
>> and 8-10% with unsigned long arithmedtic.
>> 
>> Signed-off-by: Peter Lieven <address@hidden>
>> Reviewed-by: Orit Wasserman <address@hidden>
>> Reviewed-by: Eric Blake <address@hidden>
> 
> Okay, so I bisected again and this is the second patch that is involved
> in the slowness of qemu-iotests case 007.
> 

Can you try if the following solves your issue:

diff --git a/exec.c b/exec.c
index 786987a..54baa4a 100644
--- a/exec.c
+++ b/exec.c
@@ -1071,6 +1071,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void 
*host,
             memory_try_enable_merging(new_block->host, size);
         }
     }
+    qemu_madvise(new_block->host, size, QEMU_MADV_DONTNEED);
     new_block->length = size;
 
     /* Keep the list sorted from biggest to smallest block.  */


BR,
Peter