/usr/bin/script eating 100% cpu with portupgrade and xargs

[Ronald Klop]

On Sun, 18 Sep 2011 12:58:32 +0200, Mikolaj Golub <trociny at freebsd.org>  
wrote:

>
> On Sun, 18 Sep 2011 08:47:13 +0200 Ronald Klop wrote:
>
>  RK> On Sun, 18 Sep 2011 07:39:01 +0200, Jeremy Chadwick
>  RK> <freebsd at jdc.parodius.com> wrote:
>
>  >> On Sun, Sep 18, 2011 at 12:54:13AM -0400, Jason Hellenthal wrote:
>  >>> On Sun, Sep 18, 2011 at 01:49:15AM +0200, Ronald Klop wrote:
>  >>> > Hi,
>  >>> >
>  >>> > I'm running portupgrade in screen to update all the ports for
>  >>> > 9-BETA2/9-CURRENT on amd64. While doing this script eats 100% cpu.
>  >>> > Because portupgrade -fa crashed I'm running this command to  
> update the
>  >>> > remaining non-updates ports.
>  >>> > find /var/db/pkg -name +DESC -mtime +2 |cut -d / -f 5 | xargs
>  >>> time nice -n
>  >>> > 20 portupgrade -f
>  >>> >
>  >>> > The output of truss -p `pgrep script` is this:
>  >>> > clock_gettime(13,{1316301104.000000000 })        = 0 (0x0)
>  >>> > select(5,{0 4},0x0,0x0,{30.000000 })             = 1 (0x1)
>  >>> > read(0,0x7fffffffcdf0,1024)                      = 0 (0x0)
>  >>> > write(4,0x7fffffffcdf0,0)                        = 0 (0x0)
>  >>> > clock_gettime(13,{1316301104.000000000 })        = 0 (0x0)
>  >>> > select(5,{0 4},0x0,0x0,{30.000000 })             = 1 (0x1)
>  >>> > read(0,0x7fffffffcdf0,1024)                      = 0 (0x0)
>  >>> > write(4,0x7fffffffcdf0,0)                        = 0 (0x0)
>  >>> > clock_gettime(13,{1316301104.000000000 })        = 0 (0x0)
>  >>> > select(5,{0 4},0x0,0x0,{30.000000 })             = 1 (0x1)
>  >>> > read(0,0x7fffffffcdf0,1024)                      = 0 (0x0)
>  >>> > write(4,0x7fffffffcdf0,0)                        = 0 (0x0)
>  >>> > clock_gettime(13,{1316301104.000000000 })        = 0 (0x0)
>  >>> > select(5,{0 4},0x0,0x0,{30.000000 })             = 1 (0x1)
>  >>> > read(0,0x7fffffffcdf0,1024)                      = 0 (0x0)
>  >>> > write(4,0x7fffffffcdf0,0)                        = 0 (0x0)
>  >>> >
>  >>> > So it is really fast in reading and writing 0 bytes most of the  
> time.
>  >>> >
>  >>> > I also found
>  >>> http://web.archiveorange.com/archive/v/6ETvLvjo60Gj9geAUAb6
>  >>> > and I think I am better of by rewriting my command so  
> stdin/stdout is
>  >>> > still the terminal. Although the link is a couple of years old.
>  >>> >
>  >>> > Is this known? Can somebody explain me why my xargs command is
>  >>> not working
>  >>> > well?
>  >>> >
>  >>>
>  >>> Are you absolutely sure that its script(1) causing this ? 100% CPU  
> usage
>  >>> has been a known side effect of screen(1) for quite some time.  
> Rebuild
>  >>> it and try again.
>  >>
>  >> Jason's referring to this, I believe:
>  >>  
> http://www.freebsd.org/cgi/cvsweb.cgi/ports/sysutils/screen/Makefile#rev1.55
>  >>
>  >> To clarify the what the commit message means: it does not mean "when  
> the
>  >> package is installed the installation takes up 100% CPU".  It means
>  >> "once the package is installed and screen is used, screen takes up  
> 100%
>  >> CPU".  I know because I've seen this behaviour in the past (one of  
> the
>  >> many, many reasons I build ports from source).
>  >>
>  >> However:
>  >>  
> http://www.freebsd.org/cgi/cvsweb.cgi/ports/sysutils/screen/Makefile#rev1.78
>  >>
>  >> So: If a binary package is being installed through your above
>  >> portupgrade command, and you're seeing this problem, then it sounds  
> to
>  >> me like commit revision 1.78 is a regression and NO_PACKAGE should be
>  >> put back into place + packages removed from all mirrors.
>  >>
>  >> There are many reasons to not use GNU screen at all, or if you must  
> have
>  >> something like it, use tmux.  I recently had to provide an analysis  
> of
>  >> how GNU screen destroys one's terminal[1]; so if the above problem  
> turns
>  >> out to be caused by GNU screen as well, I'll just add it to my
>  >> ever-growing list of reasons the software should be nuked from orbit.
>  >>
>  >> Otherwise, if this turns out to be a problem with portupgrade (which  
> you
>  >> found some evidence supporting such), then the solution is simple:  
> stop
>  >> using portupgrade, use portmaster (if it lacks things you need ask  
> Doug
>  >> Barton, he's incredibly receptive to adding new features/fixing  
> things).
>  >> Two databases that aren't compatible, ruby shims, and other crap =  
> not
>  >> worth it.  Think the database ordeal is long over  
> with/fixed/whatever?
>  >> It isn't[2].
>  >>
>  >> [1]:
>  >>  
> http://lists.freebsd.org/pipermail/freebsd-stable/2011-June/063052.html
>  >> [2]:
>  >>  
> http://www.dslreports.com/forum/r26304856-FreeBSD-defining-portmaster-alias
>  >>
>
>  RK> I have a repeatable test. Run top in a window and this command in  
> another.
>  RK> $ echo test | script /tmp/script-test sleep 1000
>  RK> Script started, output file is /tmp/script-test
>  RK> test
>
>  RK>   PID USERNAME       THR PRI NICE   SIZE    RES STATE   C   TIME
>  RK> CPU COMMAND
>  RK> 29656 ronald           1 103    0 12324K  1244K CPU4    4   1:03
>  RK> 100.00% script
>
>  RK> So it has nothing to do with portupgrade or screen. The output of
>  RK> truss -p29656 is the same as posted previously.
>
> I believe the behaviour is after this commit:
>
> http://svnweb.freebsd.org/base?view=revision&revision=125848
>
> I think we should skip select on STDIN after reading EOF from it, like  
> in the
> patch below.
>

It is a while since I programmed C, but why will writing 0 bytes give the  
reader an end-of-file? Shouldn't the fd be closed to indicate end-of-file?

Ronald.