[PATCH 0/6] qemu-kvm: Introduce bit-based phys_ram_dirty, and bit-based dirty page checker.

Yoshiaki Tamura
2010-03-16T10:56:20Z

The dirty and non-dirty pages are checked one by one in vl.c.
When the most of the memory is not dirty,
checking the dirty and non-dirty pages by multiple page size
should be much faster than checking them one by one.
We introduced bit-based phys_ram_dirty for VGA, CODE and MIGRATION, and
cpu_physical_memory_get_dirty_range() for this purpose.

This patch is based on the following discussion.

http://www.mail-archive.com/kvm@vger.kernel.org/msg28733.html

To prove our prospect, we have evaluated effect of this patch.
We compared runtime of ram_save_remaining with original
ram_save_remaining() and ram_save_remaining() using functions of this patch.

Test Environment:
CPU: 4x Intel Xeon Quad Core 2.66GHz
Mem size: 96GB
kvm version: 2.6.33
qemu-kvm version: commit 2b644fd0e737407133c88054ba498e772ce01f27

Host OS: CentOS (kernel 2.6.33)
Guest OS: Debian/GNU Linux lenny (kernel 2.6.26)
Guest Mem size: 512MB

Conditions of experiments are as follows:
Cond1: Guest OS periodically makes the 256MB continuous dirty pages.
Cond2: Guest OS periodically makes the 256MB dirty pages and non-dirty pages
in turn.
Cond3: Guest OS read 1GB file, which is bigger than memory.
Cond4: Guest OS write 1GB file, which is bigger than memory.

Experimental results:
Cond1: 1.9 ~ 61 times speed up
Cond2: 1.9 ~ 56 times speed up
Cond3: 1.9 ~ 59 times speed up
Cond4: 1.7 ~ 59 times speed up