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Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations |
Date: |
Wed, 14 Nov 2012 10:47:57 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121016 Thunderbird/16.0.1 |
Il 14/11/2012 10:38, liu ping fan ha scritto:
> On Tue, Nov 13, 2012 at 6:11 PM, Paolo Bonzini <address@hidden> wrote:
>>>> Il 05/11/2012 06:38, Liu Ping Fan ha scritto:
>>>>> From: Liu Ping Fan <address@hidden>
>>>>>
>>>>> If out of global lock, we will be challenged by SMP in low level,
>>>>> so need atomic ops.
>>>>>
>>>>> This file is a wrapper of GCC atomic builtin.
>>>>
>>>> I still object to this.
>>>>
>>>> I know it enforces type-safety, but it is incomplete. It doesn't
>>>
>>> Although it is incomplete, but the rest cases are rarely used. Linux
>>> faces such issue, and the "int" version is enough, so I think we can
>>> borrow experience from there.
>>
>> One of the two places that use __sync_* require 64-bit accesses. My
> Yes, these two places are not easy to fix.
Which shows that Linux's atomic_t is not suited for QEMU, in my opinion.
>> RCU prototype required pointer-sized access, which you cannot make type-
> But I think that your RCU prototype should rely on atomic of CPU, not
> gcc‘s atomic.
What's the difference? gcc's atomic produces the same instructions as
hand-written assembly (or should).
> Otherwise, it could be slow (I guess something like spinlock there).
Not sure what you mean. I'm using two things: 1) write barriers; 2)
atomic_xchg of a pointer for fast, wait-free enqueuing of call_rcu
callbacks.
Paolo
- [Qemu-devel] [PATCH v6 0/8] push mmio dispatch out of big lock, Liu Ping Fan, 2012/11/05
- [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, Liu Ping Fan, 2012/11/05
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, Paolo Bonzini, 2012/11/12
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, liu ping fan, 2012/11/13
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, Paolo Bonzini, 2012/11/13
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, liu ping fan, 2012/11/14
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, liu ping fan, 2012/11/15
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, Paolo Bonzini, 2012/11/15
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, Richard Henderson, 2012/11/15
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, liu ping fan, 2012/11/21
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, Avi Kivity, 2012/11/18
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, liu ping fan, 2012/11/21
- Re: [Qemu-devel] [PATCH v6 1/8] atomic: introduce atomic operations, Paolo Bonzini, 2012/11/13
[Qemu-devel] [PATCH v6 2/8] qom: apply atomic on object's refcount, Liu Ping Fan, 2012/11/05
[Qemu-devel] [PATCH v6 3/8] hotplug: introduce qdev_unplug_complete() to remove device from views, Liu Ping Fan, 2012/11/05