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Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory bar
From: |
Pranith Kumar |
Subject: |
Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier |
Date: |
Mon, 6 Jun 2016 11:58:04 -0400 |
On Mon, Jun 6, 2016 at 11:49 AM, Sergey Fedorov <address@hidden> wrote:
> On 06/06/16 18:47, Pranith Kumar wrote:
>> On Mon, Jun 6, 2016 at 11:44 AM, Sergey Fedorov <address@hidden> wrote:
>>> On 03/06/16 21:27, Pranith Kumar wrote:
>>>> On Thu, Jun 2, 2016 at 5:18 PM, Richard Henderson <address@hidden> wrote:
>>>>> What if we have tcg_canonicalize_memop (or some such) split off the
>>>>> barriers
>>>>> into separate opcodes. E.g.
>>>>>
>>>>> MO_BAR_LD_B = 32 // prevent earlier loads from crossing current op
>>>>> MO_BAR_ST_B = 64 // prevent earlier stores from crossing current op
>>>>> MO_BAR_LD_A = 128 // prevent later loads from crossing current op
>>>>> MO_BAR_ST_A = 256 // prevent later stores from crossing current op
>>>>> MO_BAR_LDST_B = MO_BAR_LD_B | MO_BAR_ST_B
>>>>> MO_BAR_LDST_A = MO_BAR_LD_A | MO_BAR_ST_A
>>>>> MO_BAR_MASK = MO_BAR_LDST_B | MO_BAR_LDST_A
>>>>>
>>>>> // Match Sparc MEMBAR as the most flexible host.
>>>>> TCG_BAR_LD_LD = 1 // #LoadLoad barrier
>>>>> TCG_BAR_ST_LD = 2 // #StoreLoad barrier
>>>>> TCG_BAR_LD_ST = 4 // #LoadStore barrier
>>>>> TCG_BAR_ST_ST = 8 // #StoreStore barrier
>>>>> TCG_BAR_SYNC = 64 // SEQ_CST barrier
>>>> I really like this format. I would also like to add to the frontend:
>>>>
>>> Actually, the acquire barrier is a combined load-load + load-store
>>> barrier; and the release barrier is a combo of load-store + store-store
>>> barriers.
>>>
>> All the above are two-way barriers. Acquire/Release are one-way
>> barriers. So we cannot combine the above to get acquire/release
>> semantics without being conservative.
>
> Do you mean *barriers* or *memory access* operations implying memory
> ordering?
I meant the latter. I know no arch which has acquire/release barriers.
Sorry for the confusion.
Thanks,
--
Pranith
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, (continued)
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Alex Bennée, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Pranith Kumar, 2016/06/03
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Sergey Fedorov, 2016/06/03
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Sergey Fedorov, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Pranith Kumar, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Sergey Fedorov, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier,
Pranith Kumar <=
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Sergey Fedorov, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Pranith Kumar, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Richard Henderson, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Pranith Kumar, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Sergey Fedorov, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Peter Maydell, 2016/06/06
- Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier, Sergey Fedorov, 2016/06/06