Re: [dpdk-dev] [PATCH] eal: avoid unnecessary conflicts over rte_config file

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

Hi John,

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of John Ousterhout
> Subject: Re: [dpdk-dev] [PATCH] eal: avoid unnecessary conflicts over rte_config file

<snip>

> For example, it took me several hours
> to figure out why the problem was occurring and then to hunt down the
> --file-prefix solution. Is there some reason why it would be a bad idea to
> fix this in DPDK?

Right now, DPDK will by default always use a consistent .rte_config location, which allows other applications to monitor that. For example, Collectd is able to monitor a DPDK primary process by checking if the .rte_config file exists at its default location[1].

If we change the default behavior of DPDK, other projects can no longer rely on that file being created, and these monitoring projects must be updated in sync with DPDK to avoid breakage if versions mismatch. 

Although I see your use-case, I think using the --file-prefix as Konstantin suggests is a better solution in this case.

Regards, -Harry

[1] https://github.com/collectd/collectd/blob/master/src/dpdkstat.c#L60


> On Thu, Oct 13, 2016 at 3:53 AM, Ananyev, Konstantin <
> konstantin.ananyev@intel.com> wrote:
> 
> >
> > Hi John,
> >
> > > Before this patch, DPDK used the file ~/.rte_config as a lock to detect
> > > potential interference between multiple DPDK applications running on the
> > > same machine. However, if a single user ran DPDK applications
> > concurrently
> > > on several different machines, and if the user's home directory was
> > shared
> > > between the machines via NFS, DPDK would incorrectly detect conflicts
> > > for all but the first application and abort them. This patch fixes the
> > > problem by incorporating the machine name into the config file name
> > (e.g.,
> > > ~/.rte_hostname_config).
> > >
> > > Signed-off-by: John Ousterhout <ouster@cs.stanford.edu>
> > > ---
> > >  doc/guides/prog_guide/multi_proc_support.rst | 11 +++++++----
> > >  lib/librte_eal/common/eal_common_proc.c      |  8 ++------
> > >  lib/librte_eal/common/eal_filesystem.h       | 15 +++++++++++++--
> > >  3 files changed, 22 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/doc/guides/prog_guide/multi_proc_support.rst
> > b/doc/guides/prog_guide/multi_proc_support.rst
> > > index badd102..a54fa1c 100644
> > > --- a/doc/guides/prog_guide/multi_proc_support.rst
> > > +++ b/doc/guides/prog_guide/multi_proc_support.rst
> > > @@ -129,10 +129,13 @@ Support for this usage scenario is provided using
> > the ``--file-prefix`` paramete
> > >
> > >  By default, the EAL creates hugepage files on each hugetlbfs filesystem
> > using the rtemap_X filename,
> > >  where X is in the range 0 to the maximum number of hugepages -1.
> > > -Similarly, it creates shared configuration files, memory mapped in each
> > process, using the /var/run/.rte_config filename,
> > > -when run as root (or $HOME/.rte_config when run as a non-root user;
> > > -if filesystem and device permissions are set up to allow this).
> > > -The rte part of the filenames of each of the above is configurable
> > using the file-prefix parameter.
> > > +Similarly, it creates shared configuration files, memory mapped in each
> > process.
> > > +When run as root, the name of the configuration file will be
> > > +/var/run/.rte_*host*_config, where *host* is the name of the machine.
> > > +When run as a non-root user, the the name of the configuration file
> > will be
> > > +$HOME/.rte_*host*_config (if filesystem and device permissions are set
> > up to allow this).
> > > +If the ``--file-prefix`` parameter has been specified, its value will
> > be used
> > > +in place of "rte" in the file names.
> >
> > I am not sure that we need to handle all such cases inside EAL.
> > User can easily overcome that problem by just adding something like:
> > --file-prefix=`uname -n`
> > to his command-line.
> > Konstantin
> >
> > >
> > >  In addition to specifying the file-prefix parameter,
> > >  any DPDK applications that are to be run side-by-side must explicitly
> > limit their memory use.
> > > diff --git a/lib/librte_eal/common/eal_common_proc.c
> > b/lib/librte_eal/common/eal_common_proc.c
> > > index 12e0fca..517aa0c 100644
> > > --- a/lib/librte_eal/common/eal_common_proc.c
> > > +++ b/lib/librte_eal/common/eal_common_proc.c
> > > @@ -45,12 +45,8 @@ rte_eal_primary_proc_alive(const char
> > *config_file_path)
> > >
> > >       if (config_file_path)
> > >               config_fd = open(config_file_path, O_RDONLY);
> > > -     else {
> > > -             char default_path[PATH_MAX+1];
> > > -             snprintf(default_path, PATH_MAX, RUNTIME_CONFIG_FMT,
> > > -                      default_config_dir, "rte");
> > > -             config_fd = open(default_path, O_RDONLY);
> > > -     }
> > > +     else
> > > +             config_fd = open(eal_runtime_config_path(), O_RDONLY);
> > >       if (config_fd < 0)
> > >               return 0;
> > >
> > > diff --git a/lib/librte_eal/common/eal_filesystem.h
> > b/lib/librte_eal/common/eal_filesystem.h
> > > index fdb4a70..4929aa3 100644
> > > --- a/lib/librte_eal/common/eal_filesystem.h
> > > +++ b/lib/librte_eal/common/eal_filesystem.h
> > > @@ -41,7 +41,7 @@
> > >  #define EAL_FILESYSTEM_H
> > >
> > >  /** Path of rte config file. */
> > > -#define RUNTIME_CONFIG_FMT "%s/.%s_config"
> > > +#define RUNTIME_CONFIG_FMT "%s/.%s_%s_config"
> > >
> > >  #include <stdint.h>
> > >  #include <limits.h>
> > > @@ -59,11 +59,22 @@ eal_runtime_config_path(void)
> > >       static char buffer[PATH_MAX]; /* static so auto-zeroed */
> > >       const char *directory = default_config_dir;
> > >       const char *home_dir = getenv("HOME");
> > > +     static char nameBuffer[1000];
> > > +     int result;
> > >
> > >       if (getuid() != 0 && home_dir != NULL)
> > >               directory = home_dir;
> > > +
> > > +     /*
> > > +      * Include the name of the host in the config file path. Otherwise,
> > > +      * if DPDK applications run on different hosts but share a home
> > > +      * directory (e.g. via NFS), they will choose the same config
> > > +      * file and conflict unnecessarily.
> > > +      */
> > > +     result = gethostname(nameBuffer, sizeof(nameBuffer)-1);
> > >       snprintf(buffer, sizeof(buffer) - 1, RUNTIME_CONFIG_FMT, directory,
> > > -                     internal_config.hugefile_prefix);
> > > +                     internal_config.hugefile_prefix,
> > > +             (result == 0) ? nameBuffer : "unknown-host");
> > >       return buffer;
> > >  }
> > >
> > > --
> > > 2.8.3
> >
> >