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From: Hubertus Franke <frankeh@watson.ibm.com>
Reply-To: frankeh@watson.ibm.com
Organization: IBM Research
To: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: [PATCH] get_pid() performance fix
Date: Fri, 15 Mar 2002 13:37:04 -0500
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Cc: "Rajan Ravindran" <rajancr@us.ibm.com>, linux-kernel@vger.kernel.org,
        lse-tech@lists.sourceforge.net
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On Friday 15 March 2002 10:16 am, OGAWA Hirofumi wrote:
> Whoops! I'm sorry. previous email was the middle of writing.
>
> Hubertus Franke <frankeh@watson.ibm.com> writes:
> > +	if (i == PID_MAP_SIZE) {
> > +		if (again) {
> > +			/* we didn't find any pid , sweep and try again */
> > +			again = 0;
> > +			memset(pid_map, 0, PID_MAP_SIZE * sizeof(unsigned long));
> > +			last_pid = RESERVED_PIDS;
> > +			goto repeat;
> > +		}
> > +		next_safe = RESERVED_PIDS;
> > +		return 0;
>
> Probably, the bug is here. No bug ....

>
>   +	next_safe = RESERVED_PIDS;	/* or 0 */
>
> > +	read_unlock(&tasklist_lock);
> > +	spin_unlock(&lastpid_lock);
> > +	return 0;
> >  }
>
> Basically nice, I think.
>
> BTW, How about using the __set_bit(), find_next_zero_bit(), and
> find_next_bit() in get_pid_by_map().
>
> Thanks for nice work.

OGAWA, honestly I only tried testcase 2.
But looking at your suggestion its not clear to me whether
there is a bug.
Remember we need to determine a valid interval [ last_pid .. next_safe ).
In the pid_map function, if no pid is available, then
[ PID_MAX .. PID_MAX ) will be returned.
The other path should also end up with this as well.
Could you  point where you see this not happening.

In the next release, I'll look at using your bitmap function suggestion.

-- 
-- Hubertus Franke  (frankeh@watson.ibm.com)
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