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jitv2: in sync mode, recompile a page with code only when it goes hot - #745
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With jitv2.compile = "sync" the dispatch miss compiled at every new entry on a page, so a page with many entries re-emitted itself until the code arena filled, flushed and started over. An IRIX 6.5.22 Indy never reached login that way. The sync path now asks what the threaded path asks. It compiles when the page has no code, or when this arrival is the one that makes the pending request hot; any other new entry, on a page with current or stale code, is interpreted and counted. The check is two atomic operations on the page and the existing func pointer, so the dispatch path gains no lock. An IRIX 6.5.22 Indy now reaches login with sync (285 s and 300 s on a loaded host; 145 s with the default compile mode).
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With jitv2.compile = "sync" the dispatch miss compiled at every new
entry on a page, so a page with many entries re-emitted itself until the
code arena filled, flushed and started over. An IRIX 6.5.22 Indy never
reached login that way.
The sync path now asks what the threaded path asks. It compiles when the
page has no code, or when this arrival is the one that makes the pending
request hot; any other new entry, on a page with current or stale code,
is interpreted and counted. The check is two atomic operations on the
page and the existing func pointer, so the dispatch path gains no lock.
An IRIX 6.5.22 Indy now reaches login with sync (285 s and 300 s on a
loaded host; 145 s with the default compile mode).