From: Namhyung Kim <namhyung@kernel.org>
To: Jiri Olsa <jolsa@redhat.com>
Cc: David Miller <davem@davemloft.net>,
acme@kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org,
kernel-team@lge.com
Subject: Re: [PATCH RFC] hist lookups
Date: Mon, 19 Nov 2018 14:26:03 +0900 [thread overview]
Message-ID: <20181119052603.GA20153@sejong> (raw)
In-Reply-To: <20181106115436.GE3164@krava>
Hi Jirka
Sorry for late!
On Tue, Nov 06, 2018 at 12:54:36PM +0100, Jiri Olsa wrote:
> On Mon, Nov 05, 2018 at 08:53:42PM -0800, David Miller wrote:
> >
> > Jiri,
> >
> > Because you now run queued_events__queue() lockless with that condvar
> > trick, it is possible for top->qe.in to be seen as one past the data[]
> > array, this is because the rotate_queues() code goes:
> >
> > if (++top->qe.in > &top->qe.data[1])
> > top->qe.in = &top->qe.data[0];
> >
> > So for a brief moment top->qe.in is out of range and thus
> > perf_top__mmap_read_idx() can try to enqueue to top->qe.data[2]
> >
> > We can just do:
> >
> > if (top->qe.in == &top->qe.data[1])
> > top->qe.in = &top->qe.data[0];
> > else
> > top->qe.in = &top->qe.data[1];
> >
> > Or, make top->qe.in an index, and simply go:
> >
> > top->qe.in ^= 1;
> >
> > Either way will fix the bug.
>
> ah right.. I had originaly full mutex around that,
> then I switched it off in the last patch and did
> not realize this implication.. nice ;-)
I like the rotate_queues() using cond-variable. Have you tried to use
the same for hists->lock in hists__get_rotate_entries_in() too?
Eventually it'd be nice to avoid locks when a single thread processes
all the events.
Thanks,
Namhyung
next prev parent reply other threads:[~2018-11-19 5:26 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-31 5:03 [PATCH RFC] hist lookups David Miller
2018-10-31 12:43 ` Arnaldo Carvalho de Melo
2018-10-31 15:39 ` Jiri Olsa
2018-10-31 16:08 ` David Miller
2018-11-03 6:30 ` David Miller
2018-11-04 20:18 ` Jiri Olsa
2018-11-05 0:50 ` David Miller
2018-11-05 20:34 ` Jiri Olsa
2018-11-05 22:52 ` David Miller
2018-11-06 3:45 ` David Miller
2018-11-06 4:03 ` David Miller
2018-11-06 4:53 ` David Miller
2018-11-06 11:54 ` Jiri Olsa
2018-11-19 5:26 ` Namhyung Kim [this message]
2018-11-19 9:12 ` Jiri Olsa
2018-11-20 1:13 ` Namhyung Kim
2018-11-06 20:42 ` Jiri Olsa
2018-11-07 6:13 ` David Miller
2018-11-07 8:32 ` Jiri Olsa
2018-11-07 19:43 ` Jiri Olsa
2018-11-07 20:01 ` David Miller
2018-11-07 20:28 ` Arnaldo Carvalho de Melo
2018-11-08 6:04 ` David Miller
2018-11-08 7:13 ` Jiri Olsa
2018-11-09 1:07 ` David Miller
2018-11-11 19:41 ` Jiri Olsa
2018-11-11 19:41 ` Jiri Olsa
2018-11-11 22:32 ` David Miller
2018-11-11 22:43 ` Jiri Olsa
2018-11-11 22:58 ` David Miller
2018-11-11 23:08 ` David Miller
2018-11-11 23:26 ` Jiri Olsa
2018-11-11 23:32 ` David Miller
2018-11-13 10:40 ` Jiri Olsa
2018-11-19 4:52 ` David Miller
2018-11-19 6:28 ` Namhyung Kim
2018-11-19 6:33 ` David Miller
2018-11-19 7:16 ` Namhyung Kim
2018-11-19 9:14 ` Jiri Olsa
2018-11-06 11:51 ` Jiri Olsa
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