Re: horrible disk thorughput on itanium

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Dec 07, 2001 at 12:35:22PM -0800, Ulrich Drepper wrote:
> Andreas Jaeger <aj@suse.de> writes:
> 
> > This should be doable.  We could easily implement libio/putc.c as
> > follows:
> 
> That's stupid.  Either you use putc_unlocked() as any sane person
> should in non-threaded code which then expands inline or you use
> __fsetlocking(FSETLOCKING_BYCALLER).  Just because people cannot
> program correctly doesn't require the implementation to fix their
> problems.

But cannot we really do any better to speed the thread-safe routines
locking/unlocking?

I see the
  _IO_cleanup_region_start ((void (*) __P ((void *))) _IO_funlockfile, fp);
  _IO_flockfile (fp);
  DO_SOMETHING
  _IO_funlockfile (fp);
  _IO_cleanup_region_end (0);

sequence is very common in libio, which involves (assuming no
FSETLOCKING_BYCALLER):
((fp->_flags & _IO_USER_LOCK) == 0 test
_pthread_cleanup_push_defer != NULL test (reading it from .got)
	maybe _IO_funlockfile is read from .got
	maybe _pthread_cleanup_push_defer call, through .plt
((fp->_flags & _IO_USER_LOCK) == 0 test (note that
	_pthread_cleanup_push_defer might got called, so at least
	gcc's I've tried will do this test again)
DO SOMETHING
_IO_flockfile() call through .plt
((fp->_flags & _IO_USER_LOCK) == 0 test (again, __overflow or something
	might got called)
_IO_funlockfile() call through .plt
	maybe call to _pthread_cleanup_pop_defer

Now, if e.g. fopen set some new FILE field (there is some pad AFAIK)
to function pointer which would do
_IO_cleanup_region_start and _IO_flockfile together (if needed)
and the other two calls, this could be simplified to:
{
struct lockme_buffer __buf;
fp->lockme(fp, &__buf);
DO SOMETHING
fp->unlockme(fp, &__buf);
}
or
{
struct lockme_buffer __buf;
if (fp->lockme) fp->lockme(fp, &__buf);
DO SOMETHING
if (fp->unlockme) fp->unlockme(fp, &__buf);
}

(whatever would appear to be faster). This could be even inlined.

Or, if this wouldn't make it any faster, cannot at least _IO_USER_LOCK be
set by default in fopen if not linked against -lpthread?

	Jakub