Re: [Qemu-devel] [PATCH v3 01/10] Introduce qemu_cond_timedwait for POSIX

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-04-05 15:20, malc wrote:
> On Thu, 5 Apr 2012, Jan Kiszka wrote:
> 
>> On 2012-04-05 15:00, malc wrote:
>>> On Thu, 5 Apr 2012, Jan Kiszka wrote:
>>>
>>>> On 2012-04-05 14:56, Paolo Bonzini wrote:
>>>>> Il 05/04/2012 14:53, malc ha scritto:
>>>>>> On Thu, 5 Apr 2012, Paolo Bonzini wrote:
>>>>>>
>>>>>>> Il 05/04/2012 14:30, malc ha scritto:
>>>>>>>>>> Would save that "* 1000". I just wondered why we do not use it elsewhere
>>>>>>>>>> in QEMU and was reluctant to risk some BSD breakage.
>>>>>>>>>>
>>>>>>>> It's probably worth mentioning that using anything other than 
>>>>>>>> clock_gettime and CLOCK_MONOTONING (as well as setting proper pthread
>>>>>>>> clock attr on the condition variable) is prone to the surprises (such
>>>>>>>> as NTP corrections and daylight saving changes).
>>>>>>>
>>>>>>> I was about to suggest the same, but how widespread is support for
>>>>>>> pthread_condattr_setclock?
>>>>>>
>>>>>> If it's not all is lost anyway.
>>>>>
>>>>> Only once every year. :)
>>>>
>>>> ...and not for the current user of this service which do not care that
>>>> much about the timeout and a potential delay or early shot.
>>>>
>>>
>>> An hour of potential delay mind you.
>>
>> Nope, look at posix-aio-compat. It's an optimization to keep the number
>> worker threads under control.
> 
> The code attempts to sleep for ten seconds, which can turn into an hour
> and ten seconds if the conditions are right.

Yes, but look at what happens then: it is unlikely that the thread will
stay idle so long on a busy system (some request will wake it up earlier
again), and even if that happens, the thread will simply consume a few
resources "a bit" longer.

Jan

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