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Re: [Qemu-block] [PATCH 00/13] throttle: Allow I/O bursts for a user-def

From: Stefan Hajnoczi
Subject: Re: [Qemu-block] [PATCH 00/13] throttle: Allow I/O bursts for a user-defined period of time
Date: Mon, 15 Feb 2016 16:40:29 +0000
User-agent: Mutt/1.5.24 (2015-08-30)

On Fri, Feb 05, 2016 at 12:59:10PM +0200, Alberto Garcia wrote:
>  - With this series we set "a maximum of X operations/second for a
>    period of T seconds". If would also be possible to make it "a
>    maximum of X operations/second up to a total of Y operations". It
>    would be equivalent (Y = X * T) but I thought the current proposal
>    makes a more clear API.

I find the diagram in the blog post clear.  The QEMU code is a little
harder to understand, it seems like there are too many variables and
special cases.  There are 4 core variables:

1. Refill rate (aka avg), e.g. 30 IOPS
2. Max bucket level (aka max * burst_length), e.g. 5.4 million IOPS
3. Burst rate (aka max), e.g. 3000 IOPS
4. Current bucket level

However, your patch to the core algorithm is small and makes sense to
me.  Maybe I just don't appreciate some of the subtleties that require
the existing code to use more variables.

Looks good to me.

Reviewed-by: Stefan Hajnoczi <address@hidden>

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