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@xxxxxxx>
---
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,
.
