Re: [Qemu-devel] [PATCH v2] register reset handler to write image into memory

[Yin Olivia-R63875]

Thanks to Dunrong and Andreas.

$ scripts/get_maintainer.pl -f hw/loader.c
Alexander Graf <address@hidden> (commit_signer:3/6=50%)
Anthony Liguori <address@hidden> (commit_signer:2/6=33%)
Stefan Weil <address@hidden> (commit_signer:1/6=17%)
Benjamin Herrenschmidt <address@hidden> (commit_signer:1/6=17%)
Avi Kivity <address@hidden> (commit_signer:1/6=17%)

Dear maintainers,
Could you please help review this patch?

So far I got feedback from Andreas and try to answer the question.

> This patch does not answer the question why you try to avoid the ROM blobs
> and what ROM blobs are still being used for after your patch. I don't 
> think it makes much sense to work around them for your use cases and to 
> leave them behind - if there's something fundamentally wrong with them 
> they should be ripped out completely or fixed. But maybe I'm misunderstanding 
> in the absence of explanations?

It's a general problem. 

For example, in my case, there're 3 different files loaded from host rootfs.
$ qemu-system-ppc -enable-kvm -m 256 -nographic -M mpc8544ds -kernel 
uImage.8572.agraf -initrd /media/ram/guest-8572.rootfs.ext2.gz -append 
"root=/dev/ram rw loglevel=7 console=ttyS0,115200" -serial tcp::4445,server 
-net nic

(qemu) info roms
 addr=0000000000000000 size=0x782840 mem=ram name="uImage.8572.agraf"
 addr=0000000000c00000 size=0x010000 mem=ram name="mpc8544ds.dtb"
 addr=0000000002000000 size=0x3f922f mem=ram 
name="/media/ram/guest-8572.rootfs.ext2.gz"

The problem is that rom_add_*() mallocs memory for the image, and then 
rom_reset()
copies those images into the guest's memory, but the QEMU memory does not get 
freed.
On a VM reset, the images get recopied from QEMU to guest.

Comparing the memory map of qemu process before and after starting up guest,
we can find that QEMU consumes much memory for those images.

$ diff -urN pmap.pre.log pmap.post.log
--- pmap.pre.log
+++ pmap.post.log
@@ -33,7 +33,14 @@
 0ffee000      8K rwx--  /lib/ld-2.13.so
 10000000   3472K r-x--  qemu-system-ppc
 10374000    112K rwx--  qemu-system-ppc
-10390000   6524K rwx--    [ anon ]
+10390000   7100K rwx--    [ anon ]
 48002000     16K rw---    [ anon ]
+48006000      4K -----    [ anon ]
+48007000   8188K rw---    [ anon ]
+48806000      8K rw-s-    [ anon ]
+48808000      4K rw---    [ anon ]
+48809000 262144K rw---    [ anon ]
+58809000   5280K rw---    [ anon ]
+5cb98000   7692K rw---    [ anon ]
 bf93e000    132K rw---    [ stack ]
- total    14456K
+ total   298352K

Exactly we can re-load them from disk on a reset instead of holding onto the 
images in QEMU's memory.

With this patch, the two big images (uImage and especially initrd) will not be 
loaded into QEMU's memory
(qemu) info roms
 addr=0000000000c00000 size=0x010000 mem=ram name="mpc8544ds.dtb"

It will save much memory space according to memory map of QEMU process.
# diff -urN pmap.pre.log pmap.post.log
--- pmap.pre.log
+++ pmap.post.log
@@ -33,7 +33,14 @@
 0ffee000      8K rwx--  /lib/ld-2.13.so
 10000000   3472K r-x--  qemu-system-ppc
 10374000    112K rwx--  qemu-system-ppc
-10390000   6524K rwx--    [ anon ]
+10390000   7036K rwx--    [ anon ]
 48002000     16K rw---    [ anon ]
+48006000      4K -----    [ anon ]
+48007000   8188K rw---    [ anon ]
+48806000      8K rw-s-    [ anon ]
+48808000      4K rw---    [ anon ]
+48809000 262144K rw---    [ anon ]
+58809000      4K rw---    [ anon ]
+58c04000   1204K rw---    [ anon ]
 bfb2a000    132K rw---    [ stack ]
- total    14456K
+ total   286524K

This patch changes all the image load process called by load_uimage() and 
load_image_targphys() in platform initialization.

Best Regards,
Olivia

> -----Original Message-----
> From: Dunrong Huang [mailto:address@hidden
> Sent: Thursday, August 23, 2012 6:44 PM
> To: Yin Olivia-R63875
> Cc: address@hidden; address@hidden
> Subject: Re: [Qemu-devel] [PATCH v2] register reset handler to write
> image into memory
> 
> 2012/8/23 Yin Olivia-R63875 <address@hidden>:
> > Dear All,
> >
> > I can't find MAINTAINER of hw/loader.c.
> > Who can help review and apply this patch?
> >
> Please use the script scripts/get_maintainer.pl, like:
> $ scripts/get_maintainer.pl your_patch_file.patch or
> $ scripts/get_maintainer.pl -f hw/loader.c
> > Best Regards,
> > Olivia Yin
> >
> 
> 
> --
> Best Regards,
> 
> Dunrong Huang