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Re: Re: [PATCH 1/2] MIPS: Loongson, add sync before target of branch bet

To: 徐成华 <xuchenghua@loongson.cn>
Subject: Re: Re: [PATCH 1/2] MIPS: Loongson, add sync before target of branch between llsc
From: huangpei@loongson.cn
Date: Fri, 11 Jan 2019 20:45:09 +0800 (GMT+08:00)
Cc: paul.burton@mips.com, ysu@wavecomp.com, pburton@wavecomp.com, linux-mips@vger.kernel.org, chenhc@lemote.com, zhangfx@lemote.com, wuzhangjin@gmail.com, linux-mips@linux-mips.org
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Hi all, 

    I will submit a new version patch,  which fix this bug *sufficiently and 
exactly*.

> -----原始邮件-----
> 发件人: "徐成华" <xuchenghua@loongson.cn>
> 发送时间: 2019-01-11 20:40:49 (星期五)
> 收件人: paul.burton@mips.com
> 抄送: ysu@wavecomp.com, pburton@wavecomp.com, linux-mips@vger.kernel.org, 
> chenhc@lemote.com, zhangfx@lemote.com, wuzhangjin@gmail.com, 
> linux-mips@linux-mips.org, "黄沛" <huangpei@loongson.cn>
> 主题: Re: [PATCH 1/2] MIPS: Loongson, add sync before target of branch between 
> llsc
> 
> Hi Paul Burton,
> 
> For Loongson 3A1000 and 3A3000, when a memory access instruction (load, 
> store, or prefetch)'s executing occurs between the execution of LL and SC, 
> the success or failure of SC is not predictable.  Although programmer would 
> not insert memory access instructions between LL and SC, the memory 
> instructions before LL in program-order, may dynamically executed between the 
> execution of LL/SC, so a memory fence(SYNC) is needed before LL/LLD to avoid 
> this situation.
> 
> Since 3A3000, we improved our hardware design to handle this case.  But we 
> later deduce a rarely circumstance that some speculatively executed memory 
> instructions due to branch misprediction between LL/SC still fall into the 
> above case, so a memory fence(SYNC) at branch-target(if its target is not 
> between LL/SC) is needed for 3A1000 and 3A3000.
> 
> Our processor is continually evolving and we aim to to remove all these 
> workaround-SYNCs around LL/SC for new-come processor. 
> 
> 北京市海淀区中关村环保科技示范园龙芯产业园2号楼 100095电话: +86 (10) 62546668传真: +86 (10) 
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> 
> This email and its attachments contain confidential information from Loongson
> Technology Corporation Limited, which is intended only for the person or 
> entity
> whose address is listed above. Any use of the information contained herein in
> any way (including, but not limited to, total or partial disclosure,
> reproduction or dissemination) by persons other than the intended recipient(s)
> is prohibited. If you receive this email in error, please notify the sender by
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北京市海淀区中关村环保科技示范园龙芯产业园2号楼 100095电话: +86 (10) 62546668传真: +86 (10) 
62600826www.loongson.cn本邮件及其附件含有龙芯中科技术有限公司的商业秘密信息,仅限于发送给上面地址中列出的个人或群组。禁止任何其他人以任何形式使用(包括但不限于全部或部
 分地泄露、复制或散发)本邮件及其附件中的信息。如果您错收本邮件,请您立即电话或邮件通知发件人并删除本邮件。 

This email and its attachments contain confidential information from Loongson
Technology Corporation Limited, which is intended only for the person or entity
whose address is listed above. Any use of the information contained herein in
any way (including, but not limited to, total or partial disclosure,
reproduction or dissemination) by persons other than the intended recipient(s)
is prohibited. If you receive this email in error, please notify the sender by
phone or email immediately and delete it. 
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