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   AndresFreundTec (andresfreundtec@mastodon.social)'s status on Sunday, 26-May-2024 18:04:17 JST AndresFreundTec

   Well, color me very confused. In a CPU bound workload two cores on the same socket have substantially different performance (32% slowdown). If I just migrate the running process between the cores, performance changes immediately.

   This is on 2x Xeon 5215 system.

   I checked that it's not thermals, cpu frequency/boost and the system is idle.

   Here's the odd part: The biggest difference evident in perf counters is
   a 2.5x difference in icache_64b.iftag_stall, with ~same icache_64b.iftag_miss.

   • Embed this notice
     AndresFreundTec (andresfreundtec@mastodon.social)'s status on Sunday, 26-May-2024 18:04:17 JST AndresFreundTec

     in reply to

     https://gist.github.com/anarazel/ca7d1db68fb7380d21f6fd819a147df1

     How can two cores on the same CPU such crazily different icache behaviour? For the same process!

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     AndresFreundTec (andresfreundtec@mastodon.social)'s status on Sunday, 26-May-2024 18:19:41 JST AndresFreundTec

     • Kevin Beaumont

     @GossiTheDog Hah. This is weird, but not that kind of weird, I strongly suspect.

     Although I wouldn't mind getting that farm.