Why glibc's fstat() is slow [LWN.net]

Why glibc's fstat() is slow

Posted Sep 14, 2023 19:07 UTC (Thu) by brenns10 (subscriber, #112114)
In reply to: Why glibc's fstat() is slow by wsy
Parent article: Why glibc's fstat() is slow

It's wild how many places that pops up! I fixed that in procps-ng where it would do a stat(/etc/local time) multiple times *per process* because of the printf formats being used. I'm sure tons of software, especially multithreaded apps, are experiencing this and slowdowns associated with it.

https://gitlab.com/procps-ng/procps/-/merge_requests/119

speed of repeated localtime() etc.

Posted Sep 16, 2023 0:30 UTC (Sat) by jreiser (subscriber, #11027) [Link]

Software which appends entries to a log file can call localtime (or its relatives) once per event, and there can be dozens or hundreds of events per second, for instance open(). In most cases the speed of logging can be improved by remembering the headway between the current gettimeofday() and the next future gettimeofday() when the relevant portion of localtime() can change. For an output format of HH:mm:ss, then the headway is limited to at most 1 second. For the local timezone, the minimum headway can be up to 30 minutes. If gettimeofday()still is within the headway, then there is no need to consult any any external authority.