Eric Wong <normalper...@yhbt.net> wrote:
> All relevant audio file formats store data sequentially, so
> give a hint to the kernel to perform more readahead. In current
> Linux, the readahead hint doubles readahead pages and can help
> with playback on slow devices.
Btw, I've been running this for a few years, too; but pretty
much all on FLAC.
I don't know if there's audio formats we support which aren't
sequential. Maybe there's some wacky audio format which
requires random read all over the place...
> ---
> If you prefer "git pull" instead of "git am":
>
> The following changes since commit 7e74b254b2a7c963be0bfce751fc5911fe681c12:
>
> Remove hepler script. It's mostly unmaintained, I don't know if anyone
> but me ever used it. In any case, those who want a custom Debian package
> should be capable of updating the debian/changelog entry on their own.
> (2015-02-26 22:48:40 -0500)
>
> are available in the git repository at:
>
> git://bogomips.org/sox fadvise
Nowadays moved to:
https://yhbt.net/sox.git ew/fadvise
The commit SHA-1 remains unchanged
> for you to fetch changes up to 1c47376a04218838447e7bd49fb42156e9cb13b6:
>
> use posix_fadvise to increase readahead (2015-09-07 00:39:24 +0000)
>
> ----------------------------------------------------------------
> Eric Wong (1):
> use posix_fadvise to increase readahead
>
> configure.ac | 1 +
> src/formats.c | 18 ++++++++++++++++--
> src/sox_i.h | 4 ++++
> 3 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/configure.ac b/configure.ac
> index 23138a9..d9ae1ba 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -208,6 +208,7 @@ AC_CHECK_HEADERS(fcntl.h unistd.h byteswap.h sys/stat.h
> sys/time.h sys/timeb.h s
>
> dnl Checks for library functions.
> AC_CHECK_FUNCS(strcasecmp strdup popen vsnprintf gettimeofday mkstemp
> fmemopen)
> +AC_CHECK_FUNCS(posix_fadvise)
>
> dnl Check if math library is needed.
> AC_SEARCH_LIBS([pow], [m])
> diff --git a/src/formats.c b/src/formats.c
> index 724a4cd..340b867 100644
> --- a/src/formats.c
> +++ b/src/formats.c
> @@ -329,12 +329,26 @@ static void set_endiannesses(sox_format_t * ft)
> static sox_bool is_seekable(sox_format_t const * ft)
> {
> struct stat st;
> + int fd, seekable;
>
> assert(ft);
> if (!ft->fp)
> return sox_false;
> - fstat(fileno((FILE*)ft->fp), &st);
> - return ((st.st_mode & S_IFMT) == S_IFREG);
> + fd = fileno((FILE*)ft->fp);
> + if (fd < 0)
> + return 0;
> + fstat(fd, &st);
> + seekable = ((st.st_mode & S_IFMT) == S_IFREG);
> +#if defined HAVE_POSIX_FADVISE
> + if (seekable) {
> + /*
> + * POSIX_FADV_NOREUSE can potentially be beneficial, too,
> + * but is a no-op as of Linux 4.2. Not sure about other kernels.
Still true as of Linux 5.8 :<
> + */
> + (void)posix_fadvise(fd, (off_t)0, st.st_size, POSIX_FADV_SEQUENTIAL);
Also, Linux has always ignored offset and size for
POSIX_FADV_SEQUENTIAL, so this won't do anything strange when
using the trim-as-first-effect to force seeking.
> + }
> +#endif
> + return seekable;
> }
>
> /* check that all settings have been given */
> diff --git a/src/sox_i.h b/src/sox_i.h
> index 04bbe8c..2eec9d3 100644
> --- a/src/sox_i.h
> +++ b/src/sox_i.h
> @@ -20,6 +20,10 @@
> #define _GNU_SOURCE
> #endif
>
> +#if defined HAVE_POSIX_FADVISE
> +#define _XOPEN_SOURCE 600
> +#endif
> +
I think _DEFAULT_SOURCE is needed, too, nowadays.
> #include <errno.h>
> #include <stdio.h>
> #include <stdlib.h>
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