[lxc-devel] [PATCH] /proc/stat in lxcfs

[Christian Brauner]

Hello,

/proc/stat mounted at /var/lib/lxcfs/ is currently missing
(a) the cpu average-line from the hosts /proc/stat
and
(b) the numbering of the cores starts with 1 and not with the 0.
(This will e.g.  cause confusion for top/htop in the container.) I wrote a
minimally invasive patch for that:

Signed-off-by: Christian Brauner <christianvanbrauner at gmail.com>
Date:   Sun Feb 15 10:34:41 2015 +0100

    Bring the cpu-average line to /proc/stat mounted by lxcfs and let the
    core numbering start at 0.

diff --git a/lxcfs.c b/lxcfs.c
index d6fb101..ab296e7 100644
--- a/lxcfs.c
+++ b/lxcfs.c
@@ -1642,7 +1642,7 @@ static int proc_stat_read(char *buf, size_t size, off_t offset,
    nih_local char *cpuset = NULL;
    char *line = NULL;
    size_t linelen = 0, total_len = 0;
-   int curcpu = 0;
+   int curcpu = -1; /* cpu numbering starts at 0 */
    FILE *f;
 
    if (offset)
@@ -1662,16 +1662,22 @@ static int proc_stat_read(char *buf, size_t size, off_t offset,
    while (getline(&line, &linelen, f) != -1) {
        size_t l;
        int cpu;
+        char cpu_char[10]; /* That's a lot of cores */
        char *c;
 
-       if (sscanf(line, "cpu%d", &cpu) != 1) {
-           /* not a ^cpu line, just print it */
+       if (sscanf(line, "cpu%9[^ ]", cpu_char) != 1) {
+           /* not a ^cpuN line containing a number N, just print it */
            l = snprintf(buf, size, "%s", line);
            buf += l;
            size -= l;
            total_len += l;
            continue;
        }
+        else if (sscanf(cpu_char, "%d", &cpu) != 1) {
+        }
+        else {
+        }
+
        if (!cpu_in_cpuset(cpu, cpuset))
            continue;
        curcpu ++;

Best,
Christian

> ----- Forwarded message from Serge Hallyn <serge.hallyn at ubuntu.com> -----
> 
> Date: Fri, 13 Feb 2015 04:14:11 +0000
> From: Serge Hallyn <serge.hallyn at ubuntu.com>
> To: Christian Brauner <christianvanbrauner at gmail.com>
> Subject: Re: cpusets in non-unified hierarchy broken?
> User-Agent: Mutt/1.5.21 (2010-09-15)
> 
> Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > On Thu, Feb 12, 2015 at 11:44:32PM +0000, Serge Hallyn wrote:
> > > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > > Hi Serge,
> > > > 
> > > > There is random misreporting at times from top/htop inside of the
> > > > container.  Whereas e.g. cat /proc/self/status show Cpus_allowed 0-3,
> > > > top/htop will show only 1 core.
> > > 
> > > It may be getting it from /proc/stat, which you *may* be getting through
> > > lxcfs.  It would then be filtering it through the container's cgroup
> > > info.
> > > 
> > > When you start the container, does uptime say 1 minute, or does it match
> > > the host's uptime?
> > > 
> > It says uptime 0 minutes aka it does not match the host's uptime.
> > /proc/stat is looking different in the container than on the host
> > (probably because of the cgroup filtering you mentioned).
> > 
> > I mentioned "random misreporting" mainly because the number of cores as
> > displayed by top/htop in the container does not match the number of cores on
> > the host. It is always less than on the host. I think this is caused by the
> > implementation of /proc/stat by lxcfs.
> > 
> > E.g. on the host
> > 
> >     [chb at conventiont ~]$ cat /proc/stat | grep cpu
> > 
> > will show
> > 
> >     cpu  2061 0 1623 259471 4879 0 38 0 0 0
> >     cpu0 568 0 458 63949 1905 0 12 0 0 0
> >     cpu1 584 0 371 65044 1018 0 8 0 0 0
> >     cpu2 410 0 390 65450 786 0 12 0 0 0
> >     cpu3 498 0 403 65026 1169 0 5 0 0 0
> > 
> > whereas in the container
> > 
> >     root at vivid:~# cat /proc/stat | grep cpu
> > 
> > will show
> > 
> >     cpu1  580 0 473 68799 1906 0 12 0 0 0
> >     cpu2  600 0 384 69836 1080 0 8 0 0 0
> >     cpu3  434 0 413 70268 786 0 12 0 0 0
> >     cpu4  545 0 428 69839 1169 0 5 0 0 0
> > 
> > So
> > (a) the cpu average-line from the hosts /proc/stat is missing.
> > and
> > (b) the numbering of the cores seems to be different in the container
> > 
> > I guess this causes top/htop in the container to e.g. only show three cores on
> > a four core system. Maybe, it doesn't show cpu0 at all because it thinks cpu0
> > is actually cpu (average)? Lxcfs bug maybe?
> 
> Seems very likely.  If you have time to write a patch for that that'd be
> awesome :)
> 
> (Else I'll keep it on my list)
> 
> thanks,
> -serge
> 
> ----- End forwarded message -----
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