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Re: [Qemu-trivial] [Qemu-devel] [PATCH] Use SIGIO with caution

From: Alexander Graf
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] Use SIGIO with caution
Date: Tue, 31 May 2011 18:16:15 +0200

On 31.05.2011, at 17:48, Anthony Liguori wrote:

> On 05/31/2011 10:44 AM, Alexander Graf wrote:
>> On 31.05.2011, at 16:54, Jan Kiszka wrote:
>>> On 2011-05-31 16:26, Anthony Liguori wrote:
>>>> On 05/31/2011 09:06 AM, Jan Kiszka wrote:
>>>>> On 2011-05-31 15:47, Anthony Liguori wrote:
>>>>>> On 05/29/2011 04:50 PM, Andreas Färber wrote:
>>>>>>> BeOS and Haiku don't define SIGIO. When undefined, it won't arrive
>>>>>>> and doesn't need to be blocked.
>>>>>>> Signed-off-by: Andreas Färber<address@hidden>
>>>>>> Anything to do with signal masks is never a trivial patch BTW...
>>>>>> But I actually think explicit handling of SIGIO is unneeded.  I think
>>>>>> this is a hold over from the pre-I/O thread days where we selectively
>>>>>> set SIGIO on certain file descriptors to make sure that when an IO fd
>>>>>> became readable, we received a signal to break out of the KVM emulation
>>>>>> loop.
>>>>>> Can the folks on CC confirm/deny?
>>>>>> I can't see any use of SIGIO in the current source tree.
>>>>> At least qemu-timer.c uses SIGIO in HPET mode. That only applies to
>>>>> Linux hosts, though.
>>>> Is there any reason we still carry multiple timer implementations these
>>>> days?
>>>> HPET shouldn't be any better than dynticks.
>>> On any recent kernel, for sure. BTW, the same applies to the RTC timer.
>> So the obvious change would be to introduce CONFIG_HPET, ifdef the SIGIO 
>> handling on that and also ifdef the host hpet handling code on it? That way 
>> it's documented well and can preferably even be turned off with 
>> --disable-host-hpet during configure time, which we can then slowly turn to 
>> the default.
> Or just remove hpet and rtc.
> Does anyone really object to that?

Do RHEL5 and SLES10 support dynticks? If yes, no objections. They're the oldest 
really supported distros we should possibly remotely even care about.


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