linux-kernel - Re: [PATCH v4 01/10] Use IDR to maintain all the enabled sources' paths.

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Message-ID: <059d74ef-78c2-57f2-4c14-4b20526c984c@quicinc.com>
Date:   Mon, 11 Apr 2022 10:55:50 +0800
From:   Jinlong Mao <quic_jinlmao@...cinc.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mike Leach <mike.leach@...aro.org>,
        <coresight@...ts.linaro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Tingwei Zhang <quic_tingweiz@...cinc.com>,
        Yuanfang Zhang <quic_yuanfang@...cinc.com>,
        Tao Zhang <quic_taozha@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Hao Zhang <quic_hazha@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v4 01/10] Use IDR to maintain all the enabled sources'
 paths.


On 3/30/2022 5:05 PM, Suzuki K Poulose wrote:
> On 30/03/2022 03:10, Jinlong Mao wrote:
>>
>> On 3/29/2022 10:36 PM, Mathieu Poirier wrote:
>>> On Tue, 29 Mar 2022 at 07:56, Jinlong Mao<quic_jinlmao@...cinc.com>  
>>> wrote:
>>>> Hi Suzuki,
>>>>
>>>> On 3/28/2022 4:33 PM, Suzuki K Poulose wrote:
>>>>> On 24/03/2022 14:23, Jinlong Mao wrote:
>>>>>> Hi Greg,
>>>>>>
>>>>>> Thanks for your review.
>>>>>>
>>>>>> On 3/24/2022 8:26 PM, Greg Kroah-Hartman wrote:
>>>>>>> On Thu, Mar 24, 2022 at 08:17:25PM +0800, Mao Jinlong wrote:
>>>>>>>> Use hash length of the source's device name to map to the pointer
>>>>>>>> of the enabled path. Using IDR will be more efficient than using
>>>>>>>> the list. And there could be other sources except STM and CPU etms
>>>>>>>> in the new HWs. It is better to maintain all the paths together.
>>>>>>>>
>>>>>>>> Signed-off-by: Mao Jinlong<quic_jinlmao@...cinc.com>
>>>>>>>> ---
>>>>>>>>    drivers/hwtracing/coresight/coresight-core.c | 75
>>>>>>>> +++++++-------------
>>>>>>>>    1 file changed, 26 insertions(+), 49 deletions(-)
>>>>>>> Your subject line is odd.  Please put back the driver subsystem 
>>>>>>> in the
>>>>>>> subject line so that it makes more sense.
>>>>>> I will update the subject in next version.
>>>>>>> And how have you measured "more efficient"?
>>>>>> Using IDR would be better than doing a sequential search as there
>>>>>> will be much more device  in future.
>>>>> Where do we use sequential search now ? For non-CPU bound sources, 
>>>>> yes
>>>>> we may need something. But CPU case is straight forward, and could be
>>>>> retained as it is. i.e., per-cpu list of paths.
>>>>>
>>>> We use list to store the paths for both ETM and non-CPU bound 
>>>> sources in
>>>> patch below.
>>>>
>>>> “[PATCH 01/10] coresight: add support to enable more coresight paths”
>>>>
>>>> According to Mathieu's comments, IDR is used now.  So i added 
>>>> "Using IDR
>>>> will be more efficient than using
>>>> the list" this message in my commit message. I think we need to use 
>>>> one
>>>> mechanism to store ETM and
>>>> non-CPU bound sources.
>>>>
>>>>
>>>> Mathieu's comments:
>>>>
>>>> So many TPDM and many ETMs...  That is definitely a reason to do 
>>>> better than a
>>>> sequential search.
>>>>
>>>> If an IDR (or some other kind of mechanism) is used then we can use 
>>>> that to
>>>> store paths associated with ETMs as well.  That way everything 
>>>> works the same
>>>> way and access time is constant for any kind of source.
>>> As per my last sentence above, the goal of  my comment was to simplify
>>> things so that we don't have two different ways of managing sources.
>>> But if that ends up causing more trouble than benefit then it should
>>> be avoided.
>>
>> Hi Mathieu,
>>
>> I didn't see any disadvantage to use IDR to store both ETM source and 
>> non-CPU bound sources.
>>
>> Benefits:
>>
>>   * Only need to maintain one way of managing sources.
>>   * Less time to search the path
>
> My preference is to keep the ETM source paths per-CPU. For the reasons
> below :
>   - It is straight forward for an ETM. per_cpu(paths, cpu)
>   - It is faster than the IDR.
>   - Makes the debugging easier. Simply lookup the per_cpu variable.
>
> I agree that the IDR is required for the non ETM sources. And I am fine
> with that.
>
> Suzuki

Hi Suzuki,

I will address your comments in next version.

Could you please help to review other patches ?

Thanks

Jinlong Mao

>
>>
>> Thanks
>> Jinlong Mao
>>>> Thanks
>>>>
>>>> Jinlong Mao
>>>>
>>>>> Cheers
>>>>> Suzuki
>>>>>
>>>>>
>>>>>>> thanks,
>>>>>>>
>>>>>>> greg k-h
>>>>>> Thanks
>>>>>>
>>>>>> Jinlong Mao
>>>>>>
>>> _______________________________________________
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>