linux-kernel - Re: [PATCH 3/5] iommu/vt-d: Remove unused dma map/unmap trace events

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Message-ID: <ab546a36-2403-f400-a354-edfd21795e0d@linux.intel.com>
Date:   Fri, 8 Jan 2021 08:00:00 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Will Deacon <will@...nel.org>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Guo Kaijie <Kaijie.Guo@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] iommu/vt-d: Remove unused dma map/unmap trace events

Hi Will,

On 2021/1/7 22:40, Will Deacon wrote:
> On Wed, Jan 06, 2021 at 09:14:22AM +0800, Lu Baolu wrote:
>> On 2021/1/6 3:04, Will Deacon wrote:
>>> On Thu, Dec 31, 2020 at 08:53:21AM +0800, Lu Baolu wrote:
>>>> With commit c588072bba6b5 ("iommu/vt-d: Convert intel iommu driver to
>>>> the iommu ops"), the trace events for dma map/unmap have no users any
>>>> more. Remove them so that they don't show up under
>>>> /sys/kernel/debug/tracing/events/intel_iommu. The users should use the
>>>> map/unmap traces defined in the iommu core from now on.
>>>>
>>>> Fixes: c588072bba6b5 ("iommu/vt-d: Convert intel iommu driver to the iommu ops")
>>>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>>>> ---
>>>>    include/trace/events/intel_iommu.h | 119 -----------------------------
>>>>    1 file changed, 119 deletions(-)
>>>
>>> Is this needed in 5.11, or can it wait until 5.12?
>>
>> It's necessary for 5.11 as far as I can see. Without this, users still
>> see the events under /sys/kernel/debug/tracing/events/intel_iommu, but
>> they will get nothing traced even they enable the events.
> 
> I'm just a bit wary about breaking userspace by removing them altogether,
> although I see that there's plenty of precedent for removing events from
> the include/trace/events directory, so it's probably fine.
> 
> However, the patch as-is results in this warning for me:
> 
>   | In file included from include/trace/define_trace.h:102,
>   |                  from include/trace/events/intel_iommu.h:22,
>   |                  from drivers/iommu/intel/trace.c:14:
>   | include/trace/trace_events.h:27:23: warning: ‘str__intel_iommu__trace_system_name’ defined but not used [-Wunused-const-variable=]
>   |    27 | #define __app__(x, y) str__##x##y
>   |       |                       ^~~~~
>   | include/trace/trace_events.h:28:21: note: in expansion of macro ‘__app__’
>   |    28 | #define __app(x, y) __app__(x, y)
>   |       |                     ^~~~~~~
>   | include/trace/trace_events.h:30:29: note: in expansion of macro ‘__app’
>   |    30 | #define TRACE_SYSTEM_STRING __app(TRACE_SYSTEM_VAR,__trace_system_name)
>   |       |                             ^~~~~
>   | include/trace/trace_events.h:33:20: note: in expansion of macro ‘TRACE_SYSTEM_STRING’
>   |    33 |  static const char TRACE_SYSTEM_STRING[] = \
>   |       |                    ^~~~~~~~~~~~~~~~~~~
>   | include/trace/trace_events.h:36:1: note: in expansion of macro ‘TRACE_MAKE_SYSTEM_STR’
>   |    36 | TRACE_MAKE_SYSTEM_STR();
>   |       | ^~~~~~~~~~~~~~~~~~~~~
> 
> so I'll drop this for now.

Okay, I will rework this. Thanks!

> 
> Will
> 

Best regards,
baolu