Re: [PATCH 2/4] tools headers x86: Sync msr-index.h with kernel sources

[Sandipan Das]

Hi Arnaldo,

On 8/13/2022 1:09 AM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Aug 12, 2022 at 02:33:46PM +0530, Sandipan Das escreveu:
>> Hi Jiri,
>>
>> On 8/12/2022 2:03 PM, Jiri Olsa wrote:
>>> On Thu, Aug 11, 2022 at 06:16:47PM +0530, Sandipan Das wrote:
>>>> Sync msr-index.h with the kernel sources by adding the new AMD Last Branch
>>>> Record Extension Version 2 (LbrExtV2) MSRs.
>>>>
>>>> Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
>>>> ---
>>>>  tools/arch/x86/include/asm/msr-index.h | 5 +++++
>>>>  1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/tools/arch/x86/include/asm/msr-index.h b/tools/arch/x86/include/asm/msr-index.h
>>>> index cc615be27a54..7f9eaf497947 100644
>>>> --- a/tools/arch/x86/include/asm/msr-index.h
>>>> +++ b/tools/arch/x86/include/asm/msr-index.h
>>>> @@ -574,6 +574,9 @@
>>>>  #define MSR_AMD64_PERF_CNTR_GLOBAL_CTL		0xc0000301
>>>>  #define MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR	0xc0000302
>>>>  
>>>> +/* AMD Last Branch Record MSRs */
>>>> +#define MSR_AMD64_LBR_SELECT			0xc000010e
>>>
>>> curious do we actualy use this in tools somewhere?
>>>
>>> jirka
>>>
>>
>> Commit 9dde6cadb92b ("tools arch x86: Sync the msr-index.h copy with the kernel sources")
>> from Arnaldo says that adding these new MSR definitions in the tools headers allows the
>> beautification scripts to pick up new entries which can be used for filtering MSR access
>> traces.
>>
>> E.g. one can trace the hardware LBR branch filter bits getting written to the LBR_SELECT
>> MSR while recording branches.
>>
>> $ perf record -j any,u true
>> $ perf record -j any_call,u true
>>
>> $ sudo perf trace -e msr:write_msr/max-stack=32/ --filter="msr == AMD64_LBR_SELECT"
>>
>> [...]
>> 224568.130 perf/9093 msr:write_msr(msr: AMD64_LBR_SELECT, val: 1)
>>                                        do_trace_write_msr ([kernel.kallsyms])
>>                                        do_trace_write_msr ([kernel.kallsyms])
>>                                        native_write_msr ([kernel.kallsyms])
>>                                        amd_pmu_lbr_enable_all ([kernel.kallsyms])
>>                                        amd_pmu_v2_enable_all ([kernel.kallsyms])
>>                                        x86_pmu_enable ([kernel.kallsyms])
>>                                        ctx_resched ([kernel.kallsyms])
>>                                        perf_event_exec ([kernel.kallsyms])
>>                                        begin_new_exec ([kernel.kallsyms])
>>                                        load_elf_binary ([kernel.kallsyms])
>>                                        bprm_execve ([kernel.kallsyms])
>>                                        do_execveat_common.isra.0 ([kernel.kallsyms])
>>                                        __x64_sys_execve ([kernel.kallsyms])
>>                                        do_syscall_64 ([kernel.kallsyms])
>>                                        entry_SYSCALL_64 ([kernel.kallsyms])
>>                                        execve (/usr/lib/x86_64-linux-gnu/libc.so.6)
>> [...]
>> 302748.439 perf/9126 msr:write_msr(msr: AMD64_LBR_SELECT, val: 229)
>>                                        do_trace_write_msr ([kernel.kallsyms])
>>                                        do_trace_write_msr ([kernel.kallsyms])
>>                                        native_write_msr ([kernel.kallsyms])
>>                                        amd_pmu_lbr_enable_all ([kernel.kallsyms])
>>                                        amd_pmu_v2_enable_all ([kernel.kallsyms])
>>                                        x86_pmu_enable ([kernel.kallsyms])
>>                                        ctx_resched ([kernel.kallsyms])
>>                                        perf_event_exec ([kernel.kallsyms])
>>                                        begin_new_exec ([kernel.kallsyms])
>>                                        load_elf_binary ([kernel.kallsyms])
>>                                        bprm_execve ([kernel.kallsyms])
>>                                        do_execveat_common.isra.0 ([kernel.kallsyms])
>>                                        __x64_sys_execve ([kernel.kallsyms])
>>                                        do_syscall_64 ([kernel.kallsyms])
>>                                        entry_SYSCALL_64 ([kernel.kallsyms])
>>                                        execve (/usr/lib/x86_64-linux-gnu/libc.so.6)
>> [...]
>>
>> I can add this example to the commit message in the next revision.
> 
> Right, you can reuse something from my messages updating this file or,
> better, show an example like you did above, for the thing that you are
> working at that moment :-)
> 
> One of the things we need to do is:
> 
> perf trace -e msr:write_msr/max-stack=32/ --filter-help
> 
> And then it should look what are the strings that can be used for that
> specific msr:write_msr tracepoint.
> 
> Also have tab expansion in the --filter= part :-)
> 

Thanks for the suggestions. Will incorporate them in the next revision.

- Sandipan