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SubjectRe: [PATCH v3 01/11] perf, tools: Support weak groups
On Thu, Aug 31, 2017 at 12:40:26PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> Setting up groups can be complicated due to the
> complicated scheduling restrictions of different PMUs.
> User tools usually don't understand all these restrictions.
> Still in many cases it is useful to set up groups and
> they work most of the time. However if the group
> is set up wrong some members will not reported any values
> because they never get scheduled.
>
> Add a concept of a 'weak group': try to set up a group,
> but if it's not schedulable fallback to not using
> a group. That gives us the best of both worlds:
> groups if they work, but still a usable fallback if they don't.
>
> In theory it would be possible to have more complex fallback
> strategies (e.g. try to split the group in half), but
> the simple fallback of not using a group seems to work for now.
>
> So far the weak group is only implemented for perf stat,
> not for record.
>
> Here's an unschedulable group (on IvyBridge with SMT on)
>
> % perf stat -e '{branches,branch-misses,l1d.replacement,l2_lines_in.all,l2_rqsts.all_code_rd}' -a sleep 1
>
> 73,806,067 branches
> 4,848,144 branch-misses # 6.57% of all branches
> 14,754,458 l1d.replacement
> 24,905,558 l2_lines_in.all
> <not supported> l2_rqsts.all_code_rd <------- will never report anything
>
> With the weak group:
>
> % perf stat -e '{branches,branch-misses,l1d.replacement,l2_lines_in.all,l2_rqsts.all_code_rd}:W' -a sleep 1
>
> 125,366,055 branches (80.02%)
> 9,208,402 branch-misses # 7.35% of all branches (80.01%)
> 24,560,249 l1d.replacement (80.00%)
> 43,174,971 l2_lines_in.all (80.05%)
> 31,891,457 l2_rqsts.all_code_rd (79.92%)
>
> The extra event scheduled with some extra multiplexing
>
> v2: Move fallback code to separate function.
> Add comment on for_each_group_member
> Adjust to new perf_evsel__close interface
> v3:
> Fix debug print out.
> Signed-off-by: Andi Kleen <ak@linux.intel.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

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