Patchwork [v5,7/7] Use qemu_put_buffer_async for guest memory pages

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Submitter Orit Wasserman
Date March 22, 2013, 2:48 p.m.
Message ID <1363963683-26157-8-git-send-email-owasserm@redhat.com>
Download mbox | patch
Permalink /patch/230075/
State New
Headers show

Comments

Orit Wasserman - March 22, 2013, 2:48 p.m.
This will remove an unneeded copy of guest memory pages.
For the page header and device state we still copy the data to the
static buffer the other option is to allocate the memory on demand
which is more expensive.

Signed-off-by: Orit Wasserman <owasserm@redhat.com>
---
 arch_init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Kevin Wolf - April 5, 2013, 1:44 p.m.
Am 22.03.2013 um 15:48 hat Orit Wasserman geschrieben:
> This will remove an unneeded copy of guest memory pages.
> For the page header and device state we still copy the data to the
> static buffer the other option is to allocate the memory on demand
> which is more expensive.
> 
> Signed-off-by: Orit Wasserman <owasserm@redhat.com>

This seems to have killed savevm performance. I noticed that
qemu-iotests case 007 took forever on my test box (882 seconds instead
of something like 10 seconds). It can be reproduced by this script:

export MALLOC_PERTURB_=11
qemu-img create -f qcow2 -o compat=1.1 test.qcow2 1M
time qemu-system-x86_64 -nographic -hda $TEST_IMG -serial none -monitor stdio <<EOF
savevm test
quit
EOF

This used to take about 0.6s for me, after this patch it's around 10s.

Kevin

Patch

diff --git a/arch_init.c b/arch_init.c
index 98e2bc6..aa56a20 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -481,7 +481,7 @@  static int ram_save_block(QEMUFile *f, bool last_stage)
             /* XBZRLE overflow or normal page */
             if (bytes_sent == -1) {
                 bytes_sent = save_block_hdr(f, block, offset, cont, RAM_SAVE_FLAG_PAGE);
-                qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
+                qemu_put_buffer_async(f, p, TARGET_PAGE_SIZE);
                 bytes_sent += TARGET_PAGE_SIZE;
                 acct_info.norm_pages++;
             }