Cache 的写缺失怎么理解呢
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解决时间 2021-02-15 21:35
- 提问者网友:人生佛魔见
- 2021-02-15 06:55
Cache 的写缺失怎么理解呢
最佳答案
- 二级知识专家网友:毛毛
- 2021-02-15 08:34
write back:CPU更新cache时,只是把更新的cache区标记一下,并不同步更新memory。只是在cache区要被新进入的数据取代时,才更新memory。这样做的原因是考虑到很多时候cache存入的是中间结果,没有必要同步更新memory。优点是CPU执行的效率提高,缺点是实现起来技术比较复杂。
Write-misses写缺失的处理方式
对于写操作,存在写入缓存缺失数据的情况,这时有两种处理方式:
Write allocate
(aka
Fetch on write) – Datum at the missed-write location is loaded to cache, followed by a write-hit operation. In this approach, write misses are similar to read-misses.
No-write allocate
(aka
Write-no-allocate,
Write around) – Datum at the missed-write location is not loaded to cache, and is written directly to the backing store. In this approach, actually only system reads are being cached.
Write allocate方式将写入位置读入缓存,然后采用write-hit(缓存命中写入)操作。写缺失操作与读缺失操作类似。
No-write allocate方式并不将写入位置读入缓存,而是直接将数据写入存储。这种方式下,只有读操作会被缓存。
无论是Write-through还是Write-back都可以使用写缺失的两种方式之一。只是通常Write-back采用Write allocate方式,而Write-through采用No-write allocate方式;因为多次写入同一缓存时,Write allocate配合Write-back可以提升性能;而对于Write-through则没有帮助。
Write-misses写缺失的处理方式
对于写操作,存在写入缓存缺失数据的情况,这时有两种处理方式:
Write allocate
(aka
Fetch on write) – Datum at the missed-write location is loaded to cache, followed by a write-hit operation. In this approach, write misses are similar to read-misses.
No-write allocate
(aka
Write-no-allocate,
Write around) – Datum at the missed-write location is not loaded to cache, and is written directly to the backing store. In this approach, actually only system reads are being cached.
Write allocate方式将写入位置读入缓存,然后采用write-hit(缓存命中写入)操作。写缺失操作与读缺失操作类似。
No-write allocate方式并不将写入位置读入缓存,而是直接将数据写入存储。这种方式下,只有读操作会被缓存。
无论是Write-through还是Write-back都可以使用写缺失的两种方式之一。只是通常Write-back采用Write allocate方式,而Write-through采用No-write allocate方式;因为多次写入同一缓存时,Write allocate配合Write-back可以提升性能;而对于Write-through则没有帮助。
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