Re: [Qemu-block] [PATCH v7 1/9] qcow2: Options' documentation fixes

[Alberto Garcia]

On Fri 10 Aug 2018 08:26:39 AM CEST, Leonid Bloch wrote:
> Signed-off-by: Leonid Bloch <address@hidden>
> ---
>  docs/qcow2-cache.txt | 16 +++++++++++-----
>  qemu-options.hx      |  9 ++++++---
>  2 files changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt
> index 8a09a5cc5f..0f157d859a 100644
> --- a/docs/qcow2-cache.txt
> +++ b/docs/qcow2-cache.txt
> @@ -97,12 +97,15 @@ need:
>     l2_cache_size = disk_size_GB * 131072
>     refcount_cache_size = disk_size_GB * 32768
>  
> -QEMU has a default L2 cache of 1MB (1048576 bytes) and a refcount
> -cache of 256KB (262144 bytes), so using the formulas we've just seen
> -we have
> +With the default cluster size, to cover each 8 GB of the virtual image
> +size, 1MB of L2 cache is needed:
>  
> -   1048576 / 131072 = 8 GB of virtual disk covered by that cache
> -    262144 /  32768 = 8 GB
> +   65536 / 8 = 8192 = 8 GB / 1 MB

Where does this 65536 / 8 come from? The line that you changed follows
directly from the formula immediately before that paragraph:

     l2_cache_size = disk_size_GB * 131072

that is

     l2_cache_size / 131072 = disk_size_GB
           1048576 / 131072 = 8 GB

Berto