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4682 Discussions

inconsistent back end bound values

Stefano_C_2
Beginner
164 Views

Hello,

In the attached screenshots VTune reports a back-end bound issue in the first 5 functions. When I expand the column to see the underlying category, some of them reveal no apparent issue (i.e. are not highlighted and the numeric value is equal to 0). I was wondering if it's just a bug or I should interpret the results somehow.

Thanks

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4 Replies
Stefano_C_2
Beginner
164 Views

That happens if I select to show data as bars or numeric, under the categoy Unifilled pipeline slots, both Self and Total. (only Total is shown in the screenshots)

Bernard
Black Belt
164 Views

It simply means that CPU front-end has ready to allocation uop(s) , but back-end(execution ports and execution units) cannot process those uops because of some circumstances like instruction latency or interdependencies.

By looking at screenshot highlighted function is 100% back end bound.

BTW it could be also some kind of bug because of inconsistency of the results.Highlighted function run for short period of time a few dozens of clock interrupt cycles maybe there is insufficient amount of collected data?

Stefano_C_2
Beginner
164 Views

iliyapolak wrote:

Highlighted function run for short period of time a few dozens of clock interrupt cycles maybe there is insufficient amount of collected data?



That was the problem. A longer run showed consistent results.

Thanks.

Bernard
Black Belt
164 Views

You are welcome.

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