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Date: Wed, 11 Oct 2017 04:18:57 +0800
From: "Wangnan (F)" <wangnan0@...wei.com>
To: "Liang, Kan" <kan.liang@...el.com>,
"acme@...nel.org" <acme@...nel.org>,
"peterz@...radead.org" <peterz@...radead.org>,
"mingo@...hat.com" <mingo@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "jolsa@...nel.org" <jolsa@...nel.org>,
"hekuang@...wei.com" <hekuang@...wei.com>,
"namhyung@...nel.org" <namhyung@...nel.org>,
"alexander.shishkin@...ux.intel.com"
<alexander.shishkin@...ux.intel.com>,
"Hunter, Adrian" <adrian.hunter@...el.com>,
"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH 02/10] perf tool: fix: Don't discard prev in backward mode
On 2017/10/11 3:50, Liang, Kan wrote:
>> On 2017/10/11 2:23, Wangnan (F) wrote:
>>>
>>> On 2017/10/11 1:20, kan.liang@...el.com wrote:
>>>> From: Kan Liang <kan.liang@...el.com>
>>>>
>>>> Perf record can switch output. The new output should only store the data
>>>> after switching. However, in overwrite backward mode, the new output
>>>> still have the data from old output.
>>>>
>>>> At the end of mmap_read, the position of processed ring buffer is saved
>>>> in md->prev. Next mmap_read should be end in md->prev.
>>>> However, the md->prev is discarded. So next mmap_read has to process
>>>> whole valid ring buffer, which definitely include the old processed
>>>> data.
>>>>
>>>> Set the prev as the end of the range in backward mode.
>>>>
>>>> Signed-off-by: Kan Liang <kan.liang@...el.com>
>>>> ---
>>>> tools/perf/util/evlist.c | 14 +++++++++++++-
>>>> 1 file changed, 13 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>>>> index 33b8837..7d23cf5 100644
>>>> --- a/tools/perf/util/evlist.c
>>>> +++ b/tools/perf/util/evlist.c
>>>> @@ -742,13 +742,25 @@ static int
>>>> rb_find_range(void *data, int mask, u64 head, u64 old,
>>>> u64 *start, u64 *end, bool backward)
>>>> {
>>>> + int ret;
>>>> +
>>>> if (!backward) {
>>>> *start = old;
>>>> *end = head;
>>>> return 0;
>>>> }
>>>> - return backward_rb_find_range(data, mask, head, start, end);
>>>> + ret = backward_rb_find_range(data, mask, head, start, end);
>>>> +
>>>> + /*
>>>> + * The start and end from backward_rb_find_range is the range
>>>> for all
>>>> + * valid data in ring buffer.
>>>> + * However, part of the data is processed previously.
>>>> + * Reset the end to drop the processed data
>>>> + */
>>>> + *end = old;
>>>> +
>> [SNIP]
>>
>>> If you really want to avoid record duplication, you need to changes
>>> record__mmap_read()'s
>>> logic. Now it complains "failed to keep up with mmap data" and avoid
>>> dumping data when
>>> size of newly generated data is larger than the size of the ring
>>> buffer. It is reasonable
>>> for forward ring buffer because in this case you lost the head of the
>>> first record, the
>>> whole ring buffer is unparseable. However, it is wrong in backward
>>> case. What you
>>> should do in this case is dumping the whole ring buffer.
>>>
>> I think what you want should be something like this: (not tested)
>>
> No. That's not what I want.
> My test code never trigger the WARN_ONCE.
The existing code never trigger that warning because the size computed
by rb_find_range is never larger than size of ring buffer. After applying
your patch, I believe it will trigger this WARN_ONCE and drop the whole
ring buffer. Please set a smaller ring buffer and try again.
> I think you will see the problem, if you simply run the command as below.
> sudo ./perf record -e cycles:P -C0 --overwrite --switch-output=1s
>
> The output size keep increasing. Because the new output always include the old outputs.
> What I want is the 'start' and 'end' for the increase, not everything.
This is my test result: add a '-m 1' for 'perf record' for shrinking
ring buffer,
start a while loop on CPU 0 to increase data rate.
It stops increasing after the ring buffer is full:
$:~/linux/tools/perf$ sudo ./perf record -m1 -e cycles:P -C0 --overwrite
--switch-output=1s
Warning: File /home/w00229757/.perfconfig not owned by current user
or root, ignoring it.
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2017101212165072 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2017101212165175 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2017101212165278 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2017101212165381 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2017101212165484 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2017101212165586 ]
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Dump perf.data.2017101212165653 ]
[ perf record: Captured and wrote 1.013 MB perf.data.<timestamp> ]
$ ls -l ./perf.data*
-rw------- 1 root root 538988 Oct 12 12:16 ./perf.data.2017101212165072
-rw------- 1 root root 538988 Oct 12 12:16 ./perf.data.2017101212165175
-rw------- 1 root root 538988 Oct 12 12:16 ./perf.data.2017101212165278
-rw------- 1 root root 538988 Oct 12 12:16 ./perf.data.2017101212165381
-rw------- 1 root root 538988 Oct 12 12:16 ./perf.data.2017101212165484
-rw------- 1 root root 538988 Oct 12 12:16 ./perf.data.2017101212165586
-rw------- 1 root root 1067812 Oct 12 12:16 ./perf.data.2017101212165653
You see the result keep getting larger because the ring buffer
is never full in your case.
Thank you.
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