Message ID | 1526037444-22876-3-git-send-email-ego@linux.vnet.ibm.com (mailing list archive) |
---|---|
State | Changes Requested |
Headers | show |
Series | powerpc: Scheduler optimization for POWER9 bigcores | expand |
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? > printk_once(KERN_INFO "Enabling Asymmetric SMT > scheduling\n"); > flags |= SD_ASYM_PACKING; > }
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. 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.
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
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; }