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Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory bar
From: |
Sergey Fedorov |
Subject: |
Re: [Qemu-devel] [RFC v2 PATCH 01/13] Introduce TCGOpcode for memory barrier |
Date: |
Mon, 6 Jun 2016 18:44:38 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 |
On 03/06/16 21:27, Pranith Kumar wrote:
> On Thu, Jun 2, 2016 at 5:18 PM, Richard Henderson <address@hidden> wrote:
>> Hum. That does seem helpful-ish. But I'm not certain how helpful it is to
>> complicate the helper functions even further.
>>
>> 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:
>
> MO_BAR_ACQUIRE
> MO_BAR_RELEASE
>
> and the following to the backend:
>
> TCG_BAR_ACQUIRE
> TCG_BAR_RELEASE
>
> since these are one-way barriers and the previous barrier types do not
> cover them.
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.
Kind regards,
Sergey
>
>> where
>>
>> tcg_gen_qemu_ld_i32(x, y, i, m | MO_BAR_LD_BEFORE | MO_BAR_ST_AFTER)
>>
>> emits
>>
>> mb TCG_BAR_LD_LD
>> qemu_ld_i32 x, y, i, m
>> mb TCG_BAR_LD_ST
>>
>> We can then add an optimization pass which folds barriers with no memory
>> operations in between, so that duplicates are eliminated.
>>
> Yes, folding/eliding these barriers in an optimization pass sounds
> like a good idea.
>
> Thanks,
- 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, 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, Peter Maydell, 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, 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 <=
- 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, 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, 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