Re: [Qemu-block] [Qemu-devel] [PATCH for-2.10] throttle: Make LeakyBucket.avg and LeakyBucket.max integer types

[Eric Blake]

On 08/08/2017 05:00 AM, Stefan Hajnoczi wrote:
> On Mon, Aug 07, 2017 at 07:15:29PM +0300, Alberto Garcia wrote:
>> Both the throttling limits set with the throttling.iops-* and
>> throttling.bps-* options and their QMP equivalents defined in the
>> BlockIOThrottle struct are integer values.
>>
>> Those limits are also reported in the BlockDeviceInfo struct and they
>> are integers there as well.
>>
>> Therefore there's no reason to store them internally as double and do
>> the conversion everytime we're setting or querying them, so this patch
>> uses int64_t for those types.
>>

> Why is this marked for-2.10?  Does it fix a bug?

Theoretically, converting between int64_t and double loses precision on
any values larger than 2^53.  In all practicality, though, if you expect
throttling to be precise through 2^53 (approximately 16 orders of
magnitude), you're crazy.  I also don't see any change to potential
division-by-zero actions (where differences in NaN vs. SIGFPE each have
their own advantages, but changing between them can be construed as a
bug fix).  So I'm also having a hard time seeing this as 2.10 material.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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