From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: [patch 2/2] QEMU: decrease console "refresh rate"
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Date: Tue, 15 Apr 2008 10:34:15 -0500
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Cc: kvm-devel@lists.sourceforge.net, Avi Kivity <avi@qumranet.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
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Marcelo Tosatti wrote:
> On Tue, Apr 15, 2008 at 05:45:28PM +0300, Avi Kivity wrote:
>   
>> Anthony Liguori wrote:
>>     
>>> Why did we ever need sigtimedwait() anyway?  Even if we were 
>>> select()ing within the VCPU context, we should break out of the 
>>> select() on signal delivery.
>>>
>>>       
>> select() is no good since if the signal is delivered after the select(), 
>> but before entry into guest mode, it is lost.  pselect() might work, but 
>> its is not supported on all hosts, and it (AFAICT) delivers the signals 
>> by calling their handlers, which is slow and unnecessary.
>>     
>
> Anthony tested a patch using signalfd:
>
> http://people.redhat.com/~mtosatti/io-thread-select-timeout
>
> Which is only available on newer hosts. I guess the signals will have to
> stay for older hosts.
>   

With the IO thread, we don't have to worry about lost signals like we do 
in a VCPU thread so it's fine to just use select() and install signal 
handlers IIUC.

Regards,

Anthony Liguori


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