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

[Lu Baolu <baolu.lu@linux.intel.com>]

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@linux.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