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Re: [Qemu-block] Performance impact of the qcow2 overlap checks

From: Max Reitz
Subject: Re: [Qemu-block] Performance impact of the qcow2 overlap checks
Date: Wed, 1 Feb 2017 13:08:57 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 01.02.2017 11:48, Alberto Garcia wrote:
> On Tue 31 Jan 2017 11:31:34 PM CET, Max Reitz <address@hidden> wrote:
>>> I think the checks as they are now are very simple and it's not worth
>>> complicating them too much unless we have numbers that prove that
>>> they're slowing things down. I only got those numbers for the first
>>> one.
>> I personally just think it's plain stupid to iterate through all of
>> the L1 table before every write access. It just hurts my soul.
> Right, but that's only a problem if the virtual size of the qcow2 image
> is very large, and even in that case it can be easily kept under control
> simply by increasing the cluster size.

The thing is that it should never be a problem in the first place. Why
would you increase the cluster size for a check that you actually should
not be needing anyway?


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