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From: Tong Zhang <ztong@vt.edu>
Date: Thu, 11 Feb 2016 11:39:18 -0500
Message-ID: <CAF1qENpT1WBu+vZVZVOwsVVt88XXY+zfBC_P2ygN6tLpHKgt7A@mail.gmail.com>
Subject: Re: [PATCH 1/1] Perf: fix overwritten of free running PEBSv3 timestamp
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, Arnaldo Carvalho de Melo <acme@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
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How about moving `time' to the `group', Will this help?

Regards,

Tong

Signed-off-by: Tong Zhang <ztong@vt.edu>
------
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3f590de..3163598 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -797,6 +797,7 @@ struct perf_sample_data {
        u64                             period;
        u64                             weight;
        u64                             txn;
+       u64                             time;
        union  perf_mem_data_src        data_src;

        /*
@@ -809,7 +810,6 @@ struct perf_sample_data {
                u32     pid;
                u32     tid;
        }                               tid_entry;
-       u64                             time;
        u64                             id;
        u64                             stream_id;
        struct {

On Thu, Feb 11, 2016 at 9:57 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Feb 10, 2016 at 05:38:02PM -0500, Tong Zhang wrote:
>>  commit a7b58d211ba18c9175b139e18b68c86a6bcc3c3f introduced feature of
>>  timestamp on free running PEBSv3, however, the timestamp is later
>>  overwritten, which makes the effort in vain.
>>
>> This patch fixed this problem by detecting whether timestamp is provided.
>>
>> Signed-off-by: Tong Zhang <ztong@vt.edu>
>> ---
>>  include/linux/perf_event.h  |  1 +
>>  kernel/events/core.c        | 45 +++++++++++++++++++++++++++++++++------------
>>  kernel/events/ring_buffer.c |  4 +++-
>>  3 files changed, 37 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index f9828a4..12d7b95 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -815,6 +815,7 @@ static inline void perf_sample_data_init(struct perf_sample_data *data,
>>       data->weight = 0;
>>       data->data_src.val = PERF_MEM_NA;
>>       data->txn = 0;
>> +     data->time = 0;
>>  }
>
> Argh, you just touched a new cacheline and made _every_ single event
> slower.