[Qemu-devel] Re: [PATCH 10/15] savevm: Migrate RAM based on name/offset

[Paolo Bonzini]

On 06/24/2010 06:42 AM, Alex Williamson wrote:
>           if (flags&  RAM_SAVE_FLAG_COMPRESS) {
> -            uint8_t ch = qemu_get_byte(f);
> -            memset(qemu_get_ram_ptr(addr), ch, TARGET_PAGE_SIZE);
> +            void *host;
> +            uint8_t ch;
> +
> +            if (version_id == 3) {
> +                host = qemu_get_ram_ptr(addr);
> +            } else {
> +                RAMBlock *block;
> +                char id[256];
> +                uint8_t len;
> +
> +                len = qemu_get_byte(f);
> +                qemu_get_buffer(f, (uint8_t *)id, len);
> +                id[len] = 0;

Can you measure the amount of bytes transferred before and now?  It 
seems pretty expensive.  Maybe you could add another flag so that the 
memory name is passed on the wire only if it differs from the previous 
one.  Alternatively (perhaps better) define a new kind of RAM save data 
just for the RAM block, and assume all pages after it are for that 
block.  You can even encode the RAM length in the flags, so that you 
only have to pass "len | RAM_SAVE_FLAG_BLOCK_NAME" followed by the 
length+characters of the name.

Also, code like this:

+                len = qemu_get_byte(f);
+                qemu_get_buffer(f, (uint8_t *)id, len);
+                id[len] = 0;
+
+                QLIST_FOREACH(block, &ram_list.blocks, next) {
+                    if (!strncmp(id, block->idstr, sizeof(id)))
+                        break;
+                }
+                if (!block)
+                    return -EINVAL;

is present three times.  It should be split in two functions and these 
functions be called (the first function can also be used elsewhere, I 
think, though this of course can be done in a followup).

Paolo