Re: [PATCH][RFC] Use pipe() to simulate signalfd()

[Anthony Liguori <aliguori@us.ibm.com>]

Marcelo Tosatti wrote:
> Why? If you leave data in the pipe the next select() won't block.
>
> Isnt there the possibility that this loop can be stuck for significant
> amounts of time? If you're receiving lots of notifications through
> signals.
>   

If  you're getting that many signals, then select() is never going to 
run anyway.

>>>>>> -        kvm_eat_signal(&io_signal_table, NULL, 1000);
>>>>>>        pthread_mutex_lock(&qemu_mutex);
>>>>>> -        cpu_single_env = NULL;
>>>>>> -        main_loop_wait(0);
>>>>>> +	main_loop_wait(10);
>>>>>>   
>>>>>>        
>>>>>>             
>>>>> Increase that 1000 or something. Will make it easier to spot bugs.
>>>>>
>>>>>      
>>>>>           
>>>> I have actually and it does introduce some bugs.  I'm not entirely clear 
>>>> what is causing them though.
>>>>    
>>>>         
>>> Should indicate that some event previously delivered through signals and
>>> received by sigtimedwait is not waking up the IO thread.
>>>  
>>>       
>> I'll take a look and see.  I'm having time keeping issues in the guest 
>> so it's hard to tell what problems are caused by the IO thread verses time.
>>     
>
> Time issues only with the patch? If not, please share details.
>   

No, they're independent of the patch.  The symptom is that the guest 
tends to hang during boot for prolonged periods of time.  It tends to be 
random whether it will hang at all, how long it will hang, and at what 
point it will hang.  It tends to hang more often in particular places.  
In my ubuntu server guest, for instance, it tends to hang right after 
partition probing, right after "Loading hardware drivers", and right 
before spawning a getty on /dev/tty0.

Normally, it will only hang for a few seconds.  However, with -smp N 
where N > number of cpus in the host, it tends to happen more 
frequently.  Using clock=jiffies in the guest makes the problem go away.

-no-kvm-pit doesn't make a difference (the guest is normally using the 
pm-timer).

Regards,

Anthony Liguori


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