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From:   Joel Fernandes <joelaf@google.com>
Date:   Tue, 25 Sep 2018 13:39:29 -0700
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Subject: Re: [PATCH 2/6] pstore: Add event tracing support
To:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc:     Joel Fernandes <joel@joelfernandes.org>,
        Steven Rostedt <rostedt@goodmis.org>,
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On Tue, Sep 25, 2018 at 1:37 PM, Joel Fernandes <joelaf@google.com> wrote:
> On Sun, Sep 23, 2018 at 8:33 AM, Sai Prakash Ranjan
> <saiprakash.ranjan@codeaurora.org> wrote:
>> On 9/22/2018 10:07 PM, Sai Prakash Ranjan wrote:
>>>
>>> On 9/22/2018 2:35 PM, Joel Fernandes wrote:
>>>>
>>>> On Sat, Sep 8, 2018 at 4:28 PM Sai Prakash Ranjan
>>>> <saiprakash.ranjan@codeaurora.org> wrote:
>>>>>
>>>>>
>>>>> +
>>>>> +       trace_seq_init(&iter->seq);
>>>>> +       iter->ent = fbuffer->entry;
>>>>> +       event_call->event.funcs->trace(iter, 0, event);
>>>>> +       trace_seq_putc(&iter->seq, 0);
>>>>
>>>>
>>>> Would it be possible to store the binary trace record in the pstore
>>>> buffer instead of outputting text? I suspect that will both be faster
>>>> and less space.
>>>>
>>>
>>> I will try this and come back.
>>>
>>
>> Hi Joel,
>>
>> I removed trace_seq_putc and there is some improvement seen: 203 MB/s
>>
>> # dd if=/dev/zero of=/dev/null status=progress
>> 12207371264 bytes (12 GB, 11 GiB) copied, 60 s, 203 MB/s^C
>> 24171926+0 records in
>> 24171926+0 records out
>> 12376026112 bytes (12 GB, 12 GiB) copied, 60.8282 s, 203 MB/s
>>
>> This seems good when compared to 190 MB/s seen previously.
>> If this is Ok, then I will spin v2 with changes suggested.
>
> Sorry for slow reply, yes that sounds good and a worthwhile perf improvement.
>

Well so I think you should still not use spinlock to synchronize and
split the buffer. You could expand pstore_record to have a ts field or
introduce a new API like ->write_percpu instead of write, or
something. But I strongly feel you should lock. For ftrace function
trace, the perf reduction with locking was dramatic.

- Joel