{"action":"created","comment":{"url":"https://api.github.com/repos/lowRISC/lowrisc-site/pulls/comments/116023304","pull_request_review_id":37607498,"id":116023304,"diff_hunk":"@@ -37,21 +35,22 @@ However, we can increase it further.\n \n ## General concept of a hierarchical tag cache\n \n-In this release, we implemented an optimised hierarchical tag cache to\n-compress the empty (unset) tags cached in the tag cache.\n-This compression is based on the observation that most of the memory is not tagged for most use cases.\n-It is likely that most of the tags cached are zero or empty in normal operation condition.\n-To utilise this pattern, a hierarchical cache uses a bit-map to record the emptiness of each cached tag cache line.\n-When a whole line is empty (0), the emptiness state stored in the bit-map is enough to fully represent the cache line;\n-therefore, the actual empty line is no long need to be cached (no need to access it from memory as well).\n+In this release, we observe that most of the memory is not tagged for most use cases.\n+Therefore, we can implement optimisation based on an hierarchical tag cache to\n+compress the unset tags cached in the tag cache.\n+It is likely that most of the tags cached are unset in normal operation condition.\n+By analogy with the cache lines of recently used code, tag cache lines contain recently used tags.\n+A tag cache line is just a normal cache line in the tag cache; however, this cache line stores tags rather than data.\n+To utilise this pattern, a hierarchical cache uses a bit-map to record the presence of any cached tag cache line.\n+When a whole line is unused, the bit-map is enough to fully represent the cache line;\n+therefore, the actual unused line is no long needed to be cached (no need to access it from memory as well).","path":"content/docs/minion-v0.4/tag_cache.md","position":32,"original_position":32,"commit_id":"99f64cb92ca696496672e9bdfcfdfc2d9335c6bb","original_commit_id":"99f64cb92ca696496672e9bdfcfdfc2d9335c6bb","user":{"login":"wsong83","id":821840,"avatar_url":"https://avatars1.githubusercontent.com/u/821840?v=3","gravatar_id":"","url":"https://api.github.com/users/wsong83","html_url":"https://github.com/wsong83","followers_url":"https://api.github.com/users/wsong83/followers","following_url":"https://api.github.com/users/wsong83/following{/other_user}","gists_url":"https://api.github.com/users/wsong83/gists{/gist_id}","starred_url":"https://api.github.com/users/wsong83/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/wsong83/subscriptions","organizations_url":"https://api.github.com/users/wsong83/orgs","repos_url":"https://api.github.com/users/wsong83/repos","events_url":"https://api.github.com/users/wsong83/events{/privacy}","received_events_url":"https://api.github.com/users/wsong83/received_events","type":"User","site_admin":false},"body":"We cannot really say it is unused. A tag of 0 may be the actual value needed by a program. In this case, the cache line is used, but there is no needed to store it in the tag cache.","created_at":"2017-05-11T15:32:32Z","updated_at":"2017-05-11T15:36:44Z","html_url":"https://github.com/lowRISC/lowrisc-site/pull/25#discussion_r116023304","pull_request_url":"https://api.github.com/repos/lowRISC/lowrisc-site/pulls/25","_links":{"self":{"href":"https://api.github.com/repos/lowRISC/lowrisc-site/pulls/comments/116023304"},"html":{"href":"https://github.com/lowRISC/lowrisc-site/pull/25#discussion_r116023304"},"pull_request":{"href":"https://api.github.com/repos/lowRISC/lowrisc-site/pulls/25"}}},"pull_request":{"url":"https://api.github.com/repos/lowRISC/lowrisc-site/pulls/25","id":120053356,"html_url":"https://github.com/lowRISC/lowrisc-site/pull/25","diff_url":"https://github.com/lowRISC/lowrisc-site/pull/25.diff","patch_url":"https://github.com/lowRISC/lowrisc-site/pull/25.patch","issue_url":"https://api.github.com/repos/lowRISC/lowrisc-site/issues/25","number":25,"state":"open","locked":false,"title":"Rob tag review","user":{"login":"jrrk","id":525783,"avatar_url":"https://avatars1.githubusercontent.com/u/525783?v=3","gravatar_id":"","url":"https://api.github.com/users/jrrk","html_url":"https://github.com/jrrk","followers_url":"https://api.github.com/users/jrrk/followers","following_url":"https://api.github.com/users/jrrk/following{/other_user}","gists_url":"https://api.github.com/users/jrrk/gists{/gist_id}","starred_url":"https://api.github.com/users/jrrk/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jrrk/subscriptions","organizations_url":"https://api.github.com/users/jrrk/orgs","repos_url":"https://api.github.com/users/jrrk/repos","events_url":"https://api.github.com/users/jrrk/events{/privacy}","received_events_url":"https://api.github.com/users/jrrk/received_events","type":"User","site_admin":false},"body":"Attempt to capture feedback from various emails, and some contradictory information. 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