Messages in this thread | | | Date | Thu, 29 Jun 2023 14:04:06 +0200 | Subject | Re: [PATCH v2 0/9] Introduce SMT level and add PowerPC support | From | Laurent Dufour <> |
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Le 29/06/2023 à 13:10, Michael Ellerman a écrit : > Sachin Sant <sachinp@linux.ibm.com> writes: >>> On 28-Jun-2023, at 3:35 PM, Laurent Dufour <ldufour@linux.ibm.com> wrote: >>> >>> I'm taking over the series Michael sent previously [1] which is smartly >>> reviewing the initial series I sent [2]. This series is addressing the >>> comments sent by Thomas and me on the Michael's one. >>> >>> Here is a short introduction to the issue this series is addressing: >>> >>> When a new CPU is added, the kernel is activating all its threads. This >>> leads to weird, but functional, result when adding CPU on a SMT 4 system >>> for instance. >>> >>> Here the newly added CPU 1 has 8 threads while the other one has 4 threads >>> active (system has been booted with the 'smt-enabled=4' kernel option): >>> >>> ltcden3-lp12:~ # ppc64_cpu --info >>> Core 0: 0* 1* 2* 3* 4 5 6 7 >>> Core 1: 8* 9* 10* 11* 12* 13* 14* 15* >>> >>> This mixed SMT level may confused end users and/or some applications. >>> >> >> Thanks for the patches Laurent. >> >> Is the SMT level retained even when dynamically changing SMT values? >> I am observing difference in behaviour with and without smt-enabled >> kernel command line option. >> >> When smt-enabled= option is specified SMT level is retained across >> cpu core remove and add. >> >> Without this option but changing SMT level during runtime using >> ppc64_cpu —smt=<level>, the SMT level is not retained after >> cpu core add. > > That's because ppc64_cpu is not using the sysfs SMT control file, it's > just onlining/offlining threads manually. > > If you run: > $ ppc64_cpu --smt=4 > > And then also do: > > $ echo 4 > /sys/devices/system/cpu/smt/control > > It should work as expected? > > ppc64_cpu will need to be updated to do that automatically.
Hi Sachin and Michael,
Yes, ppc64_cpu will need an update, and I have a patch ready to be sent once this series will be accepted.
By the way, I've a fix for the build issue reported against the patch 6/9. I'll send a v3 soon.
Cheers,
Laurent.
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