Re: [PATCH 2/2] powerpc: Enable ASYM_SMT on interleaved big-core systems
Gautham R Shenoy 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" >> > >> > 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 >> > --- >> > 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
Re: [PATCH 2/2] powerpc: Enable ASYM_SMT on interleaved big-core systems
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" > > > > 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 > > --- > > 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. 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 -- Thanks and Regards gautham.
Re: [PATCH 2/2] powerpc: Enable ASYM_SMT on interleaved big-core systems
On Fri, 2018-05-11 at 16:47 +0530, Gautham R. Shenoy wrote: > From: "Gautham R. Shenoy" > > 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 > --- > 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? > printk_once(KERN_INFO "Enabling Asymmetric SMT > scheduling\n"); > flags |= SD_ASYM_PACKING; > }
[PATCH 2/2] powerpc: Enable ASYM_SMT on interleaved big-core systems
From: "Gautham R. Shenoy" 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 --- 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) { printk_once(KERN_INFO "Enabling Asymmetric SMT scheduling\n"); flags |= SD_ASYM_PACKING; } -- 1.9.4