Armaan Sandhu
79e32e7c73
sd_journal_next() sweeps every open journal file to find the next entry, and next_beyond_location() rate-limits its tail timestamp refresh per file. Since ratelimit_below() reads the clock itself, iterating a journal spread over a hundred files meant a hundred clock_gettime() calls for every single entry, nearly all of them only to conclude that the one second interval had not elapsed yet. On a 730M journal in 100 files this was the single largest cost in journalctl, over a fifth of the run. Add ratelimit_below_at(), which takes the timestamp from the caller, and read the clock once per sweep in real_journal_next() instead. ratelimit_below() keeps its behaviour and becomes a wrapper. The timestamp is now sampled once for the whole sweep rather than once per file. The interval being rate-limited is a second and a sweep takes microseconds, so this makes no practical difference. On that journal, journalctl -o export goes from 4.02s to 2.93s, and the default journalctl -o short from 3.30s to 2.14s.
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