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请教关于缓存中T权限的设计 #152

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user-stu-l opened this issue Oct 14, 2023 · 2 comments
Open

请教关于缓存中T权限的设计 #152

user-stu-l opened this issue Oct 14, 2023 · 2 comments

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@user-stu-l
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您好，我发现在L1Cache中请求NtoB,很多情况下L2cache的D通道会自动升权到toT响应，在Dcache中应该是没问题的，但是在多核ICache情况在，ICache正常情况下应该只读，但是T权限是可读可写，那按我的理解多核情况下icache频繁的probe toB,那这样性能上是不是会有问题呢？请问当时设计的promoteT是基于哪些方面的考虑呢？谢谢！
@wakafa1
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wakafa1 commented Oct 26, 2023

给 L1I 响应的时候如果默认 promoteT，确实有可能会在自修改代码密度高的 workload 中降低性能；目前最新昆明湖架构不再硬件维护 L1I 的一致性，已经解决了这一问题

@user-stu-l
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好的，谢谢！不过还是不太理解为什么要设计req_promoteT？在阅读代码的过程中发现，promoteT_safe这个条件好像可有可无，请问它触发的场景有哪些呢？

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@wakafa1 @user-stu-l