Extremely slooooow __sys_ftruncate?

[Kostik Belousov]

On Thu, Mar 20, 2008 at 08:48:17PM -0700, Kip Macy wrote:
> "truncate" may be synchronous on FreeBSD - almost nothing is on Linux.
Partial truncate is synchronous for UFS mounts. Full truncate (to 0 lenght)
also may become synchronous under high i/o pressure.

> 
>    -Kip
> 
> On Thu, Mar 20, 2008 at 8:02 PM, Steve Kargl
> <sgk at troutmask.apl.washington.edu> wrote:
> > In the process of helping to debug a problem with gcc-4.4.0
> >  (actually a gfortran problem), I run gprof on the executable.
> >  The profile shows that __sys_ftruncate is extremely slow.
> >
> >   %   cumulative   self              self     total
> >   time   seconds   seconds    calls  ms/call  ms/call  name
> >   85.6       6.05     6.05    51830     0.12     0.12  __sys_ftruncate [2]
> >   5.6       6.44     0.40        0  100.00%           .mcount (101)
> >   1.7       6.56     0.12    51872     0.00     0.00  _lseek [5]
> >   1.6       6.67     0.11    52055     0.00     0.00  sigprocmask [6]
> >   0.8       6.73     0.06   103687     0.00     0.00  memset [14]
> >   0.4       6.76     0.03      488     0.06     0.06  __sys_write [18]
> >   0.4       6.79     0.03        0  100.00%           formatted_transfer_scalar
> >
> >  time ./z
> >      184.21 real         0.98 user         6.57 sys
> >
> >  This program should finish well under 184 seconds.  The same program
> >  and exact same gcc/gfortran source on linux shows
> >   real    0m0.555s    user    0m0.103s    sys     0m0.452s
> >
> >  Is __sys_ftruncate known to have performance problems?
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