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Re: [Qemu-devel] [PATCH 1.1] coroutine: Avoid ucontext usage on i386 Lin

From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH 1.1] coroutine: Avoid ucontext usage on i386 Linux host
Date: Wed, 09 May 2012 17:11:21 -0300
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

On 2012-05-09 17:01, Anthony Liguori wrote:
> On 05/09/2012 02:57 PM, Jan Kiszka wrote:
>> On 2012-05-09 16:48, Anthony Liguori wrote:
>>> On 05/09/2012 02:34 PM, Jan Kiszka wrote:
>>>>> Can't we resort to the SIGUSR1 workaround for the time being, while
>>>>> no RT signals are in actual use, and just have the time to let the
>>>>> kernel side to fix the things up before some actual RTsig user will
>>>>> emerge in qemu?  I think it is a bit more conservative approach,
>>>>> especially having in mind the minority of users this issue affects
>>>>> (only 32/64 mixed environment).  I'd favor for this variant, and
>>>>> it looks like I'm the "main" 32/64bit user of qemu in this world :)
>>>> Most conservative is definitely this patch, not switching to SIGUSR1,
>>>> hoping that no other RT signal user shows up until current kernel are no
>>>> longer in use.
>>> Sorry, how is using a totally different code path more conservative than 
>>> using a
>>> different signal number?
>> If the gthread version is not safe to use, why do we fall back to it?
> It's safe, but it's significantly slower.

OK. Then what about sigaltstack (once fixed)? Is it also slower? If not,
can we converge over it? I would really hate staying with this time bomb
of broken RT signals unless someone tells me we will kick out all these
coroutines rather sooner than later.


Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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