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

[Jan Kiszka]

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.

Jan

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