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Re: [Qemu-devel] [PATCH v11 5/9] qcow2: Assign the L2 cache relatively t

From: Alberto Garcia
Subject: Re: [Qemu-devel] [PATCH v11 5/9] qcow2: Assign the L2 cache relatively to the image size
Date: Tue, 25 Sep 2018 14:10:28 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Tue 25 Sep 2018 12:53:53 AM CEST, Leonid Bloch wrote:
> Now, the L2 cache assignment is aware of the virtual size of the
> image, and will cover the entire image, unless the cache size needed
> for that is larger than a certain maximum. This maximum is set to 1 MB
> by default (enough to cover an 8 GB image with the default cluster
> size) but can be increased or decreased using the 'l2-cache-size'
> option.

Previously the maximum was "1MB or 8 clusters", now it's always
1MB. This means that:

  - If you cluster size is 2MB the maximum is not actually 1MB (unless
    you reduce the cache entry size).

  - For cluster sizes > 128KB this patch reduces the default cache size.

Now, I don't think any of these things is very important because you're
increasing the default size in a subsequent patch, so I don't think you
need change this patch. You can add brief comment summarizing this in
the commit message if you want, but I'm ok if you leave it unchanged.

There's still the case that (after increasing the upper limit) for
non-Linux platforms the L2 cache size is reduced from 16MB to 8MB if you
have 2MB clusters. But since in this case an 8MB L2 cache is enough for
a 2TB image, so I don't think it's that important.

Reviewed-by: Alberto Garcia <address@hidden>


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