[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only fo
From: |
Jan Kiszka |
Subject: |
Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now) |
Date: |
Wed, 26 Oct 2011 17:13:25 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
On 2011-10-26 17:09, Peter Maydell wrote:
> On 26 October 2011 16:02, Jan Kiszka <address@hidden> wrote:
>> On 2011-10-26 16:54, Peter Maydell wrote:
>>> On 26 October 2011 15:39, Paolo Bonzini <address@hidden> wrote:
>>>> On 10/26/2011 04:03 PM, Peter Maydell wrote:
>>>>>
>>>>> For the record (since I think we only talked about this on IRC):
>>>>> * the POSIX TLS fallback code doesn't work on Linux hosts for
>>>>> linux-user emulation (the constructor is never called to set up
>>>>> the TLS for the main thread, probably something to do with our
>>>>> custom linker script, since it does work OK for system emulation)
>>>>> * if I recall correctly from IRC it doesn't compile on OpenBSD
>>>>>
>>>>> so for 1.0 perhaps we need to fall back to a simpler set of patches
>>>>> that just avoid the regression in thread support for linux-user ?
>>>>
>>>> I agree.
>>>
>>> I was thinking something like a trivial qemu-tls.h which does
>>>
>>> #ifdef __linux__
>>> #define DECLARE_TLS(type, x) extern DEFINE_TLS(type, x)
>>> #define DEFINE_TLS(type, x) __thread __typeof__(type) tls__##x
>>> #define get_tls(x) tls__##x
>>> #else
>>> /* Dummy implementations -- we can get away with this because system
>>> * mode is effectively single-threaded for our current limited use of
>>> * TLS, and the only -user mode which supports multiple threads is
>>> * linux-user.
>>
>> We will use it in system mode as well, e.g. when I'll push away the
>> global lock from KVM entry/exits. So let's state that it is only
>> interesting on Linux hosts for now.
>>
>> Otherwise, this looks good.
>
> The point of the comment is that you can't use this facility in
> system mode until we've added the non-Linux support (because you'd
> break Win32 &c). So fixing and committing the non-Linux support is
> a prerequisite for anything like the global lock moves. I can be
> a bit more explicit about that if you like:
>
> /* Dummy implementations -- we can get away with this because system
> * mode is effectively single-threaded for our current limited use of
> * TLS, and the only -user mode which supports multiple threads is
> * linux-user.
> * This means you cannot use this for any variables which will
> * actually be accessed by more than one thread in system mode
> * until the implementations for Win32 and POSIX systems without
> * __thread have been added!
> *
> * TODO: add implementations via Win32 .tls sections and
> * POSIX pthread_getspecific.
> */
>
> -- PMM
My point is that it is fine to use for per-vcpu variables because:
- they are single-threaded in TCG mode
- they are multi-threaded in KVM mode, but that's only affecting Linux
hosts for which this TLS wrapper is already usable
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), (continued)
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Peter Maydell, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Paolo Bonzini, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Peter Maydell, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Paolo Bonzini, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Jan Kiszka, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Peter Maydell, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now),
Jan Kiszka <=
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Peter Maydell, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Jan Kiszka, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Andreas Färber, 2011/10/26
- Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now), Jan Kiszka, 2011/10/26