From: burke@... Date: 2017-03-28T19:46:10+00:00 Subject: [ruby-core:80437] [Ruby trunk Feature#13378] Eliminate 4 of 8 syscalls when requiring file by absolute path Issue #13378 has been reported by burke (Burke Libbey). ---------------------------------------- Feature #13378: Eliminate 4 of 8 syscalls when requiring file by absolute path https://bugs.ruby-lang.org/issues/13378 * Author: burke (Burke Libbey) * Status: Open * Priority: Normal * Assignee: * Target version: ---------------------------------------- Don't open file twice when specified by absolute path. When invoking `require '/a.rb'` (i.e. via an absolute path), ruby generates this sequence of syscalls: open /a.rb fstat64 /a.rb close /a.rb open /a.rb fstat64 /a.rb fstat64 /a.rb read /a.rb close /a.rb It is apparent that the only inherently necessary members of this sequence are: open /a.rb fstat64 /a.rb read /a.rb close /a.rb (the fstat64 isn't *obviously* necessary, but it does serve a purpose and probably shouldn't be removed). The first open/fstat64/close is used to check whether the file is loadable. This is important when scanning the `$LOAD_PATH`, since it is used to determine when a file has been found. However, when we've already unambiguously identified a file before invoking `require`, this serves no inherent purpose, since we can move whatever work is happening as a result of that `fstat64` into the second open/close sequence. This change bypasses the first open/fstat64/close in the case of an absolute path to `require`. It also removes one of the doubled-up `fstat64` calls later in the sequence. As a result, the number of syscalls to require a file changes: * From 8 to 4 when specified by absolute path; * From 5+3n to 4+3n otherwise *(where n is the number of `$LOAD_PATH` items scanned)*. In future work, it would be possible to re-use the file descriptor opened while searching the `$LOAD_PATH` without the close/open sequence, but this would cause some ugly layering issues. --- *We intend to use this in conjunction with something like https://github.com/shopify/bootscale, which pre-resolves required features to absolute paths before calling `require`. This change reduces our total number of filesystem accesses by 13% during application boot.* *Various notes and rationale at http://notes.burke.libbey.me/ruby-require-optimization* ---Files-------------------------------- 0001-reduce-syscalls-on-require.patch (7.56 KB) -- https://bugs.ruby-lang.org/ Unsubscribe: