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From: Steven Rostedt <rostedt@goodmis.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jiri Olsa <jolsa@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	<linux-trace-users@vger.kernel.org>
Subject: Re: [RFC][PATCH 2/4] tracing: Use pid bitmap instead of a pid array for set_event_pid
Date: Fri, 22 Apr 2016 11:30:19 -0400	[thread overview]
Message-ID: <20160422113019.5b2d5cc8@gandalf.local.home> (raw)
In-Reply-To: <20160422024530.GA1790@sejong>

On Fri, 22 Apr 2016 11:45:30 +0900
Namhyung Kim <namhyung@kernel.org> wrote:

> > +	pid_list->pid_max = READ_ONCE(pid_max);
> > +	/* Only truncating will shrink pid_max */
> > +	if (filtered_pids && filtered_pids->pid_max > pid_list->pid_max)
> > +		pid_list->pid_max = filtered_pids->pid_max;
> > +	pid_list->pids = vzalloc((pid_list->pid_max + 7) >> 3);
> > +	if (!pid_list->pids) {
> > +		kfree(pid_list);
> > +		read = -ENOMEM;
> > +		goto out;
> > +	}
> > +	if (filtered_pids) {
> > +		/* copy the current bits to the new max */
> > +		pid = find_first_bit(filtered_pids->pids,
> > +				     filtered_pids->pid_max);
> > +		while (pid < filtered_pids->pid_max) {
> > +			set_bit(pid, pid_list->pids);
> > +			pid = find_next_bit(filtered_pids->pids,
> > +					    filtered_pids->pid_max,
> > +					    pid + 1);
> > +			nr_pids++;
> > +		}  
> 
> Why not just use memcpy and keep nr_pids in the pid_list?

This is the slow path (very slow ;-), and this was the first method
that came to my mind (while I programmed this during a conference). I
could use memcpy, or simply one of the bitmask copies, and then get the
nr_pids from bitmask_weight(). I would not keep nr_pids in pid_list
because that would mean that I would have to manage it in the fast path.

Maybe later I'll convert it to bitmap_copy(), but for now I'll just
keep it as is. I move this code in my queue for 4.8, and don't want to
deal with conflicts unless there's a real bug discovered.

Thanks for looking at this code!

-- Steve


  parent reply	other threads:[~2016-04-22 15:30 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-19 14:34 [RFC][PATCH 0/4] tracing: Add event-fork to trace tasks children Steven Rostedt
2016-04-19 14:34 ` [RFC][PATCH 1/4] tracing: Rename check_ignore_pid() to ignore_this_task() Steven Rostedt
2016-04-19 14:34 ` [RFC][PATCH 2/4] tracing: Use pid bitmap instead of a pid array for set_event_pid Steven Rostedt
     [not found]   ` <1694657549.62933.1461084928341.JavaMail.zimbra@efficios.com>
2016-04-19 17:19     ` Steven Rostedt
     [not found]       ` <4ACF15B6-D344-4647-9CF8-CEDE5BF5EF70@zytor.com>
2016-04-19 19:41         ` Steven Rostedt
     [not found]           ` <2093660141.63332.1461097049611.JavaMail.zimbra@efficios.com>
2016-04-19 20:50             ` Steven Rostedt
     [not found]               ` <568915868.63547.1461100941927.JavaMail.zimbra@efficios.com>
2016-04-19 22:49                 ` Steven Rostedt
     [not found]                   ` <2099338042.63665.1461106754326.JavaMail.zimbra@efficios.com>
2016-04-19 23:06                     ` Steven Rostedt
     [not found]   ` <20160422024530.GA1790@sejong>
2016-04-22 15:30     ` Steven Rostedt [this message]
2016-04-19 14:34 ` [RFC][PATCH 3/4] tracing: Add infrastructure to allow set_event_pid to follow children Steven Rostedt
     [not found]   ` <1887707510.62932.1461084911586.JavaMail.zimbra@efficios.com>
2016-04-19 17:13     ` Steven Rostedt
2016-04-19 14:34 ` [RFC][PATCH 4/4] tracing: Update the documentation to describe "event-fork" option Steven Rostedt
     [not found] ` <5716E3E8.7000609@redhat.com>
2016-04-20  2:30   ` [RFC][PATCH 0/4] tracing: Add event-fork to trace tasks children Steven Rostedt

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