linux-kernel - Re: [PATCH] coresight: docs: Remove target sink from examples

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <50e4aab7-d262-48a0-b956-2c2df0faeb25@linaro.org>
Date: Tue, 17 Dec 2024 17:17:01 +0000
From: James Clark <james.clark@...aro.org>
To: scclevenger@...amperecomputing.com, coresight@...ts.linaro.org
Cc: yeoreum.yun@....com, Mike Leach <mike.leach@...aro.org>,
 Jonathan Corbet <corbet@....net>, Leo Yan <leo.yan@...ux.dev>,
 Namhyung Kim <namhyung@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: docs: Remove target sink from examples



On 12/12/2024 7:38 pm, Steve Clevenger wrote:
> 
> 
> On 12/12/2024 7:27 AM, James Clark wrote:
>>
>>
>> On 11/12/2024 6:01 pm, Steve Clevenger wrote:
>>>
>>> Hi James,
>>>
>>> I thought I'd mention this issue with multicore self-hosted trace. The
>>> perf command line syntax does not allow a sink "type" to be specified
>>> (e.g. @tmc_etf or @tmc_etr). For multicore, it doesn't make sense to
>>> specify a processor mapped sink as would be the case for single core
>>> trace. A sink "type" should be allowed to avoid the auto select default.
>>> In our case, the default is the ETF sink.
>>>
>>> Thanks,
>>> Steve C.
>>>
>>
>> I'm sure it would be possible to add support for this, but I'm wondering
>> if the real issue is that the default selection logic is wrong? Are you
>> saying the default you get is ETF but you want ETR? And there is both
>> for each ETM? The default selection logic isn't easy to summarize but it
>> should prefer ETR (sysmem) over ETF (link sink), see coresight_find_sink().
>>
>> It's probably better to fix that rather than add a new sink selection
>> feature. Maybe if you shared a diagram of your coresight architecture it
>> would help.
>>
>> Thanks
>> James
> 
> Hi James,
> 
> It appears the default sink selection is ETF for multicore trace. In any
> case, for the Arm® CoreSight Base System Architecture STC Level
> compliance, I need to be able to specify the sink type.

Yep it makes sense to add support for selecting it then then, I will put 
it on the list but not sure about the priority. I think looking into why 
the default isn't working is more important for now.

> 
> The Ampere CoreSight hierarchy is described to the ACPI as follows:
> 
> 
> +-----------------+
> |                 |
> |       ETM       |
> |                 |
> +--------+--------+
>           |
>           |
> +--------+--------+
> |                 |
> |       ETF       |
> |                 |
> +--------+--------+
>           |
>           |
> +--------+--------+
> |                 |
> |       ETR       |
> |                 |
> +--------+--------+
>           |
>           |
> +--------+--------+
> |                 |
> |      CATU       |
> |                 |
> +--------+--------+
> 
> Steve C.
> 

I recreated this in the test here: 
https://lore.kernel.org/linux-kernel/20241217171132.834943-1-james.clark@linaro.org/T/#u

But it looks like it correctly selects ETR rather than ETF, so I'm not 
sure what the difference is between your setup and that. If you can have 
a look at that test and compare it that would be very helpful.

Thanks
James