Re: [PATCH] perf, script: Minimize "not reaching sample" for brstackinsn

[Adrian Hunter <adrian.hunter@intel.com>]

On 29/02/24 01:33, Andi Kleen wrote:
>>> There are two common cases where the message is bogus:
>>> - The LBR only logs taken branches, but the branch might be a
>>> conditional branch that is not taken (that is the most common
>>> case actually)
>>
>> How do you know it is not a taken branch that missed the LBR update?
> 
> I don't, but the not taken case is totally valid (and also common)
> so it doesn't make sense to have a mere sanity check make a common
> case unusable.
> 
>>
>>> - The LBR sampling uses a filter ignoring some branches,
>>> but the perf script check checks for all branches.
>>
>> Not understanding this case.  Do you mean you expect not to reach
>> the sample, so there is no point printing the message?
> 
> If the LBR is e.g. filtered on far branches it makes no sense to 
> check for non far branches. There are lot of filtering cases here which
> would be very complicated to handle for a mere sanity check,
> so the best way is to not do the bogus sanity check.

This comment could be updated

	 * between final branch and sample. When this happens just
	 * continue walking after the last TO until we hit a branch.

It's not clear why "attr->branch_sample_type == 0" is there.