Spawning threads in KVM/QEMU

Spawning threads in KVM/QEMU

[Anthony Liguori]

Hi,

I've been experimenting with creating IO threads for the PV device 
drivers.  Unfortunately, my experiments haven't gotten very far as QEMU 
tends to hang up a bit into booting the guest whenever I spawn a thread 
that does any sort of read/write on a file descriptor.  My suspicion is 
that it has something to do with signals being delivered to the wrong 
thread but after masking out all the signals for this thread, I still 
had no luck.

Any clues to what may be going on?

Regards,

Anthony Liguori

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Re: Spawning threads in KVM/QEMU

[Dor Laor]

Anthony Liguori wrote:
> Hi,
>
> I've been experimenting with creating IO threads for the PV device 
> drivers.  Unfortunately, my experiments haven't gotten very far as QEMU 
> tends to hang up a bit into booting the guest whenever I spawn a thread 
> that does any sort of read/write on a file descriptor.  My suspicion is 
> that it has something to do with signals being delivered to the wrong 
> thread but after masking out all the signals for this thread, I still 
> had no luck.
>
>   
Maybe you set the mask too late? try setting it before creating the thread:
 sigfillset(&thread_sig_mask);
 sigdelset(&thread_sig_mask,SIGILL);
 sigdelset(&thread_sig_mask,SIGFPE);
 sigdelset(&thread_sig_mask,SIGSEGV);
 pthread_sigmask(SIG_SETMASK, &thread_sig_mask, &curr_sig_mask);
 if ((r = pthread_create(&thread_tid, NULL, thread_func, &init_data))) {
    ....
  }
 pthread_sigmask(SIG_SETMASK, &curr_sig_mask, NULL);
> Any clues to what may be going on?
>
> Regards,
>
> Anthony Liguori
>
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>
>   


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Re: Spawning threads in KVM/QEMU

[Luca Tettamanti]

On Nov 13, 2007 11:42 PM, Dor Laor <dor.laor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Anthony Liguori wrote:
> > I've been experimenting with creating IO threads for the PV device
> > drivers.  Unfortunately, my experiments haven't gotten very far as QEMU
> > tends to hang up a bit into booting the guest whenever I spawn a thread
> > that does any sort of read/write on a file descriptor.  My suspicion is
> > that it has something to do with signals being delivered to the wrong
> > thread but after masking out all the signals for this thread, I still
> > had no luck.
> >
> Maybe you set the mask too late? try setting it before creating the thread:
>  sigfillset(&thread_sig_mask);
>  sigdelset(&thread_sig_mask,SIGILL);
>  sigdelset(&thread_sig_mask,SIGFPE);
>  sigdelset(&thread_sig_mask,SIGSEGV);

When using RTC or HPET for timing you also need to mask SIGIO; you may
also need to change F_SETOWN (enable_sigio_timer) with the correct
thread id, i.e.:

fcntl(fd, F_SETOWN, gettid());

Luca

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Re: Spawning threads in KVM/QEMU

[Dor Laor]

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Luca Tettamanti wrote:
> On Nov 13, 2007 11:42 PM, Dor Laor <dor.laor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>   
>> Anthony Liguori wrote:
>>     
>>> I've been experimenting with creating IO threads for the PV device
>>> drivers.  Unfortunately, my experiments haven't gotten very far as QEMU
>>> tends to hang up a bit into booting the guest whenever I spawn a thread
>>> that does any sort of read/write on a file descriptor.  My suspicion is
>>> that it has something to do with signals being delivered to the wrong
>>> thread but after masking out all the signals for this thread, I still
>>> had no luck.
>>>
>>>       
>> Maybe you set the mask too late? try setting it before creating the thread:
>>  sigfillset(&thread_sig_mask);
>>  sigdelset(&thread_sig_mask,SIGILL);
>>  sigdelset(&thread_sig_mask,SIGFPE);
>>  sigdelset(&thread_sig_mask,SIGSEGV);
>>     
>
> When using RTC or HPET for timing you also need to mask SIGIO; you may
> also need to change F_SETOWN (enable_sigio_timer) with the correct
> thread id, i.e.:
>
> fcntl(fd, F_SETOWN, gettid());
>
> Luca
>
>   
I do mask SIGIO - first the set is fiilled, then SGILL,SIGFPE,SIGSEGV 
are back enabled.
Regards, Dor

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Re: Spawning threads in KVM/QEMU

[Avi Kivity]

Dor Laor wrote:
> Anthony Liguori wrote:
>   
>> Hi,
>>
>> I've been experimenting with creating IO threads for the PV device 
>> drivers.  Unfortunately, my experiments haven't gotten very far as QEMU 
>> tends to hang up a bit into booting the guest whenever I spawn a thread 
>> that does any sort of read/write on a file descriptor.  My suspicion is 
>> that it has something to do with signals being delivered to the wrong 
>> thread but after masking out all the signals for this thread, I still 
>> had no luck.
>>
>>   
>>     
> Maybe you set the mask too late? try setting it before creating the thread:
>  sigfillset(&thread_sig_mask);
>  sigdelset(&thread_sig_mask,SIGILL);
>  sigdelset(&thread_sig_mask,SIGFPE);
>  sigdelset(&thread_sig_mask,SIGSEGV);
>  pthread_sigmask(SIG_SETMASK, &thread_sig_mask, &curr_sig_mask);
>  if ((r = pthread_create(&thread_tid, NULL, thread_func, &init_data))) {
>     ....
>   }
>  pthread_sigmask(SIG_SETMASK, &curr_sig_mask, NULL);
>   

Actually when running with kvm, most signals are blocked while running 
in userspace.  They're only enabled when the guest is running.  So no 
special action should be necessary.

For pure qemu, it is necessary of course.



-- 
error compiling committee.c: too many arguments to function


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