Date: Tue, 2 Apr 2024 15:16:37 +0200
To: cygwin@cygwin.com
Subject: Re: Cygwin&Win32 file prefetch, block sizes?
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From: Corinna Vinschen via Cygwin <cygwin@cygwin.com>
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On Apr  2 02:04, Martin Wege via Cygwin wrote:
> Hello,
> 
> Is there any document which describes how Cygwin and Win32 file
> prefetch and readahead work, and which sizes are used (e.g. always
> read one full page even if only 16 bytes are requested?)?

I'm not aware of any docs, but again, keep in mind that Cygwin is a
usersapce DLL. We basically do what Windows does for low-level file
access.

> Quick /usr/bin/stat /etc/profile returns "IO Block: 65536". Does that
> mean the file's block size is really 64k? Is this info per filesystem,
> or hardcoded in Cygwin?

Hardcoded in Cygwin since 2017, based on a discussion in terms of
file access performance, especially when using stdio.h functions:

  https://cygwin.com/cgit/newlib-cygwin/commit/?id=7bef7db5ccd9c

Corinna

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