Re: horrible disk thorughput on itanium

[Andreas Jaeger <aj at suse dot de>]

I'm bringing over this discussion from linux-kernel to libc-alpha, I'm
not CC'ing linux-kernel anymore since that list is irrelevant for this
topic.

torvalds@transmeta.com (Linus Torvalds) writes:

> In article <Pine.LNX.4.33.0112070710120.747-100000@mikeg.weiden.de>,
> Mike Galbraith  <mikeg@wen-online.de> wrote:
>>
>>> Andrew Morton <akpm@zip.com.au> writes:
>>>
>>> As far as I can see bonnie++ doesn't use putc_unlocked, but putc.
>>
>>Plain old Bonnie suffered from the same thing.  I long ago made it
>>use putc_unlocked() here because throughput was horrible otherwise.
>
> Oh, yeah, blame it on bonnie.
>
> 	"Our C library 'putc' is horribly sucky"
>
> 	"Well, then, use something else then".
>
> Isn't somebody ashamed of glibc and willing to try to fix it? It might
> be as simple as just testing a static flag "have I used pthread_create"
> or even a function pointer that gets switched around at pthread_create..

This should be doable.  We could easily implement libio/putc.c as
follows:

extern void __pthread_initialize (void) __attribute__ ((weak));

int
_IO_putc (c, fp)
     int c;
     _IO_FILE *fp;
{
  if (__pthread_initialize != NULL)
    {
      int result;
      CHECK_FILE (fp, EOF);
      _IO_cleanup_region_start ((void (*) __P ((void *))) _IO_funlockfile, fp);
      _IO_flockfile (fp);
      result = _IO_putc_unlocked (c, fp);
      _IO_funlockfile (fp);
      _IO_cleanup_region_end (0);
      return result;
    }
  return _IO_putc_unlocked (c, fp);
}

The cost for code that is linked against libpthread is an extra
comparison.  Code that does not use libpthread will be faster since we
don't need to do the locking.

As an alternative we could used instead of __pthread_initialize a symbol:
weak_extern (__pthreads_in_use)

and set this in pthread_create.

What do others think?  Shall I send a complete patch?

Andreas
-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj