09-13-2011
POSIX specifies programming APIs. It is silent on the implementation of those APIs.
However, the behavior you see if what I would expect. Writes by their very nature are going to take longer than reads. Reads can come from cache. Writes cannot.
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LEARN ABOUT PHP
sd-readahead
SD-READAHEAD(7) sd-readahead SD-READAHEAD(7)
NAME
sd-readahead - Reference implementation of APIs for controlling boot-time read-ahead
SYNOPSIS
#include "sd-readahead.h"
DESCRIPTION
sd-readahead.c and sd-readahead.h provide a reference implementation for APIs for controlling boot-time read-ahead, as implemented by the
read-ahead subsystem of the systemd(1) init system.
See sd_readahead(3) for more information about the function implemented.
NOTES
This interface is provided by the reference implementation of APIs for controlling boot-time read-ahead and distributed with the systemd
package. The algorithms it implements are simple, and can easily be reimplemented in daemons if it is important to support this interface
without using the reference implementation. See the respective function man pages for details.
In addition, for details about the algorithms check the liberally licensed reference implementation sources:
http://cgit.freedesktop.org/systemd/systemd/plain/src/readahead/sd-readahead.c resp.
http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-readahead.h
These APIs are implemented in the reference implementation's drop-in sd-readahead.c and sd-readahead.h files. It is recommended that
applications consuming these APIs copy the implementation into their source tree, either verbatim or in excerpts. These interfaces are
currently not available in a dynamic library.
The functions provided by this interface become NOPs when -DDISABLE_SYSTEMD is set during compilation. In addition, if sd-readhead.c is
compiled on non-Linux systems it becomes NOPs.
SEE ALSO
systemd(1), sd_readahead(3), sd-daemon(7)
AUTHOR
Lennart Poettering <lennart@poettering.net>
Developer
systemd 03/16/2012 SD-READAHEAD(7)