| Message ID | 20190523224015.56270-3-jeremy.linton@arm.com (mailing list archive) |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
| Series | arm64/PPTT ACPI 6.3 thread flag support | expand |
On 23/05/2019 23:40, Jeremy Linton wrote: > ACPI 6.3 adds a thread flag to represent if a CPU/PE is > actually a thread. Given that the MPIDR_MT bit may not > represent this information consistently on homogeneous machines > we should prefer the PPTT flag if its available. > Hi Jeremy, I was just wondering if we should look to get this support backported (when merged)? I worry about the case of a system with the CPU having MT bit in the MPIDR (while not actually threaded), i.e. the system for which these PPTT flags were added (as I understand). > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> > --- > arch/arm64/kernel/topology.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 0825c4a856e3..cbbedb53cf06 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -346,11 +346,9 @@ void remove_cpu_topology(unsigned int cpu) > */ > static int __init parse_acpi_topology(void) > { > - bool is_threaded; > + int is_threaded; > int cpu, topology_id; > > - is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; > - > for_each_possible_cpu(cpu) { > int i, cache_id; > > @@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void) > if (topology_id < 0) > return topology_id; > > + is_threaded = acpi_pptt_cpu_is_thread(cpu); > + if (is_threaded < 0) > + is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; > + > if (is_threaded) { > cpu_topology[cpu].thread_id = topology_id; For described above scenario, this seems wrong. > topology_id = find_acpi_cpu_topology(cpu, 1); > BTW, we did test an old kernel with 6.3 PPTT bios for this on D06 (some versions have MT bit set), and it looked ok. But I am still a bit skeptical. Thanks, John
Hi, Thanks for testing and looking at this. On 6/6/19 3:49 AM, John Garry wrote: > On 23/05/2019 23:40, Jeremy Linton wrote: >> ACPI 6.3 adds a thread flag to represent if a CPU/PE is >> actually a thread. Given that the MPIDR_MT bit may not >> represent this information consistently on homogeneous machines >> we should prefer the PPTT flag if its available. >> > > Hi Jeremy, > > I was just wondering if we should look to get this support backported > (when merged)? I imagine that will happen.. > > I worry about the case of a system with the CPU having MT bit in the > MPIDR (while not actually threaded), i.e. the system for which these > PPTT flags were added (as I understand). I have tested this patch on DAWN which happens to have the MT bit set, but isn't threaded, and it appears to work. > >> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> >> --- >> arch/arm64/kernel/topology.c | 8 +++++--- >> 1 file changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c >> index 0825c4a856e3..cbbedb53cf06 100644 >> --- a/arch/arm64/kernel/topology.c >> +++ b/arch/arm64/kernel/topology.c >> @@ -346,11 +346,9 @@ void remove_cpu_topology(unsigned int cpu) >> */ >> static int __init parse_acpi_topology(void) >> { >> - bool is_threaded; >> + int is_threaded; >> int cpu, topology_id; >> >> - is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; >> - >> for_each_possible_cpu(cpu) { >> int i, cache_id; >> >> @@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void) >> if (topology_id < 0) >> return topology_id; >> >> + is_threaded = acpi_pptt_cpu_is_thread(cpu); >> + if (is_threaded < 0) >> + is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; >> + >> if (is_threaded) { >> cpu_topology[cpu].thread_id = topology_id; > > For described above scenario, this seems wrong. I'm not sure I understand the concern. This is going to ignore the MPIDR_MT bit on any machine with a PPTT revision > 1. Are you worried about the topology_id assignment? > >> topology_id = find_acpi_cpu_topology(cpu, 1); >> > > BTW, we did test an old kernel with 6.3 PPTT bios for this on D06 (some > versions have MT bit set), and it looked ok. But I am still a bit > skeptical. > > Thanks, > John > > Thanks,
On 07/06/2019 20:21, Jeremy Linton wrote: > Hi, > > Thanks for testing and looking at this. > > On 6/6/19 3:49 AM, John Garry wrote: >> On 23/05/2019 23:40, Jeremy Linton wrote: >>> ACPI 6.3 adds a thread flag to represent if a CPU/PE is >>> actually a thread. Given that the MPIDR_MT bit may not >>> represent this information consistently on homogeneous machines >>> we should prefer the PPTT flag if its available. >>> >> Hi Jeremy, >> >> I was just wondering if we should look to get this support backported >> (when merged)? > > I imagine that will happen.. > >> >> I worry about the case of a system with the CPU having MT bit in the >> MPIDR (while not actually threaded), i.e. the system for which these >> PPTT flags were added (as I understand). > > I have tested this patch on DAWN which happens to have the MT bit set, > but isn't threaded, and it appears to work. Can you describe your test? > >> >>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> >>> --- >>> arch/arm64/kernel/topology.c | 8 +++++--- >>> 1 file changed, 5 insertions(+), 3 deletions(-) >>> >>> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c >>> index 0825c4a856e3..cbbedb53cf06 100644 >>> --- a/arch/arm64/kernel/topology.c >>> +++ b/arch/arm64/kernel/topology.c >>> @@ -346,11 +346,9 @@ void remove_cpu_topology(unsigned int cpu) >>> */ >>> static int __init parse_acpi_topology(void) >>> { >>> - bool is_threaded; >>> + int is_threaded; >>> int cpu, topology_id; >>> >>> - is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; >>> - >>> for_each_possible_cpu(cpu) { >>> int i, cache_id; >>> >>> @@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void) >>> if (topology_id < 0) >>> return topology_id; >>> >>> + is_threaded = acpi_pptt_cpu_is_thread(cpu); >>> + if (is_threaded < 0) >>> + is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; >>> + >>> if (is_threaded) { >>> cpu_topology[cpu].thread_id = topology_id; >> >> For described above scenario, this seems wrong. > > I'm not sure I understand the concern. Maybe I wasn't clear enough previously. I am saying that without this patch, then this info would not be correct. Hence the request to backport to stable. cheers, > > This is going to ignore the MPIDR_MT bit on any machine with a PPTT > revision > 1. Are you worried about the topology_id assignment? > > >> >>> topology_id = find_acpi_cpu_topology(cpu, 1); >>> >> >> BTW, we did test an old kernel with 6.3 PPTT bios for this on D06 >> (some versions have MT bit set), and it looked ok. But I am still a >> bit skeptical. >> >> Thanks, >> John >> >> > > > Thanks, > > . >
Hi, On 6/10/19 3:30 AM, John Garry wrote: > On 07/06/2019 20:21, Jeremy Linton wrote: >> Hi, >> >> Thanks for testing and looking at this. >> >> On 6/6/19 3:49 AM, John Garry wrote: >>> On 23/05/2019 23:40, Jeremy Linton wrote: >>>> ACPI 6.3 adds a thread flag to represent if a CPU/PE is >>>> actually a thread. Given that the MPIDR_MT bit may not >>>> represent this information consistently on homogeneous machines >>>> we should prefer the PPTT flag if its available. >>>> >>> > > Hi Jeremy, > >>> >>> I was just wondering if we should look to get this support backported >>> (when merged)? >> >> I imagine that will happen.. >> >>> >>> I worry about the case of a system with the CPU having MT bit in the >>> MPIDR (while not actually threaded), i.e. the system for which these >>> PPTT flags were added (as I understand). >> >> I have tested this patch on DAWN which happens to have the MT bit set, >> but isn't threaded, and it appears to work. > > Can you describe your test? The positive test: Boot machine with/without patch, compare the output of lscpu & lstopo. Manually check/compare /sys/devices/system/cpu/cpuX/topology/* and /proc/schedstat domain masks. On DAWN we go from a system reporting 2 cores with 2 thread per core to 4 cores. I've also built firmware or injected PPTT's with varying versions/etc to sanity check cases that aren't representative of the hardware. > >> >>> >>>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> >>>> --- >>>> arch/arm64/kernel/topology.c | 8 +++++--- >>>> 1 file changed, 5 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/arch/arm64/kernel/topology.c >>>> b/arch/arm64/kernel/topology.c >>>> index 0825c4a856e3..cbbedb53cf06 100644 >>>> --- a/arch/arm64/kernel/topology.c >>>> +++ b/arch/arm64/kernel/topology.c >>>> @@ -346,11 +346,9 @@ void remove_cpu_topology(unsigned int cpu) >>>> */ >>>> static int __init parse_acpi_topology(void) >>>> { >>>> - bool is_threaded; >>>> + int is_threaded; >>>> int cpu, topology_id; >>>> >>>> - is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; >>>> - >>>> for_each_possible_cpu(cpu) { >>>> int i, cache_id; >>>> >>>> @@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void) >>>> if (topology_id < 0) >>>> return topology_id; >>>> >>>> + is_threaded = acpi_pptt_cpu_is_thread(cpu); >>>> + if (is_threaded < 0) >>>> + is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; >>>> + >>>> if (is_threaded) { >>>> cpu_topology[cpu].thread_id = topology_id; >>> >>> For described above scenario, this seems wrong. >> >> I'm not sure I understand the concern. > > Maybe I wasn't clear enough previously. I am saying that without this > patch, then this info would not be correct. Hence the request to > backport to stable. > > cheers, > >> >> This is going to ignore the MPIDR_MT bit on any machine with a PPTT >> revision > 1. Are you worried about the topology_id assignment? >> >> >>> >>>> topology_id = find_acpi_cpu_topology(cpu, 1); >>>> >>> >>> BTW, we did test an old kernel with 6.3 PPTT bios for this on D06 >>> (some versions have MT bit set), and it looked ok. But I am still a >>> bit skeptical. >>> >>> Thanks, >>> John >>> >>> >> >> >> Thanks, >> >> . >> > >
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index 0825c4a856e3..cbbedb53cf06 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -346,11 +346,9 @@ void remove_cpu_topology(unsigned int cpu) */ static int __init parse_acpi_topology(void) { - bool is_threaded; + int is_threaded; int cpu, topology_id; - is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; - for_each_possible_cpu(cpu) { int i, cache_id; @@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void) if (topology_id < 0) return topology_id; + is_threaded = acpi_pptt_cpu_is_thread(cpu); + if (is_threaded < 0) + is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK; + if (is_threaded) { cpu_topology[cpu].thread_id = topology_id; topology_id = find_acpi_cpu_topology(cpu, 1);
ACPI 6.3 adds a thread flag to represent if a CPU/PE is actually a thread. Given that the MPIDR_MT bit may not represent this information consistently on homogeneous machines we should prefer the PPTT flag if its available. Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> --- arch/arm64/kernel/topology.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)