Re: [Qemu-devel] [Qemu-block] [PATCH 6/7] qemu-iotests: 141: reduce likelihood of race condition on systems with fast IO

[Sascha Silbe]

Dear Max,

Max Reitz <address@hidden> writes:

> On 05.04.2016 11:21, Sascha Silbe wrote:
>> On systems with fast IO, qemu-io may write more than 1 MiB before
>> receiving the block-job-cancel command, causing the test case to fail.
>> 
>> 141 is inherently racy, but we can at least reduce the likelihood of the
>> job completing before the cancel command arrives by bumping the size of
>> the data getting written; we'll try 32 MiB for a start.
>
> Hm, interesting. I tried to prevent this by setting the block jobs'
> speed to 1, which should make it stop after the block job has processed
> the first block of data.

Hmm, seems like I didn't quite understand the way the test works
then.

@Kevin: Please do NOT queue this patch.

@Max: From a cursory glance at the code, maybe your 1 *byte* per second
rate limit is being rounded down to 0 *blocks* per second, with 0
meaning no limit? See e.g. mirror_set_speed(). Though I must admit I
don't understand how speed=0 translates to unlimited (like
qapi/block-core.json:block-job-set-speed says). My understanding of
ratelimit_calculate_delay() is that speed=0 means "1 quantum per time
slice", with time slice usually being 100ms; not sure about the
quantum.

Sascha
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