From: Christian Weisgerber <naddy@mips.inka.de>
Subject: Re: optimise reading the file index
To: gameoftrees@openbsd.org
Date: Thu, 27 Jul 2023 15:19:47 +0200

Stefan Sperling:

> mmap is probably faster than the current code only because with mmap we are
> asking the kernel to read page-sized blocks from the file, instead of tiny
> amounts like sizeof(uint32_t), sizeof(uint64_t) sized-chunks. (Not sure what
> the minimun size of a read in the kernel is, probably a 512 bytes sector?
> Could be less than a page.)

The current code uses fread(3), i.e., buffered stdio, which translates
to a long series of 16 kB read(2) system calls.

For a got status of /usr/src, 786 read(2) calls look rather negligible
compared to 92,300+ stat(2) calls.

-- 
Christian "naddy" Weisgerber                          naddy@mips.inka.de