Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH 2/2] powerpc: Enable ASYM_SMT on interleaved big-core systems | Date | Fri, 18 May 2018 23:05:57 +1000 |
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Gautham R Shenoy <ego@linux.vnet.ibm.com> writes:
> On Mon, May 14, 2018 at 01:22:07PM +1000, Michael Neuling wrote: >> On Fri, 2018-05-11 at 16:47 +0530, Gautham R. Shenoy wrote: >> > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> >> > >> > Each of the SMT4 cores forming a fused-core are more or less >> > independent units. Thus when multiple tasks are scheduled to run on >> > the fused core, we get the best performance when the tasks are spread >> > across the pair of SMT4 cores. >> > >> > Since the threads in the pair of SMT4 cores of an interleaved big-core >> > are numbered {0,2,4,6} and {1,3,5,7} respectively, enable ASYM_SMT on >> > such interleaved big-cores that will bias the load-balancing of tasks >> > on smaller numbered threads, which will automatically result in >> > spreading the tasks uniformly across the associated pair of SMT4 >> > cores. >> > >> > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> >> > --- >> > arch/powerpc/kernel/smp.c | 2 +- >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c >> > index 9ca7148..0153f01 100644 >> > --- a/arch/powerpc/kernel/smp.c >> > +++ b/arch/powerpc/kernel/smp.c >> > @@ -1082,7 +1082,7 @@ static int powerpc_smt_flags(void) >> > { >> > int flags = SD_SHARE_CPUCAPACITY | SD_SHARE_PKG_RESOURCES; >> > >> > - if (cpu_has_feature(CPU_FTR_ASYM_SMT)) { >> > + if (cpu_has_feature(CPU_FTR_ASYM_SMT) || has_interleaved_big_core) { >> >> Shouldn't we just set CPU_FTR_ASYM_SMT and leave this code > unchanged? > > Yes, that would have the same effect. I refrained from doing that > since I thought CPU_FTR_ASYM_SMT has the "lower numbered threads > expedite thread-folding" connotation from the POWER7 generation.
The above code is the only use of the feature, so I don't think we need to worry about any other connotations.
> If it is ok to overload CPU_FTR_ASYM_SMT, we can do what you suggest > and have all the changes in setup-common.c
Yeah let's do that.
cheers
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