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

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Date:   Tue, 29 Mar 2022 08:36:55 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Jinlong Mao <quic_jinlmao@...cinc.com>
Cc:     Suzuki K Poulose <Suzuki.Poulose@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...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 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.

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