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s390/topology: alternative topology for topology-less machines

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If running on machines that do not provide topology information we
currently generate a "fake" topology which defines the maximum
distance between each cpu: each cpu will be put into an own drawer.

Historically this used to be the best option for (virtual) machines in
overcommited hypervisors.

For some workloads however it is better to generate a different
topology where all cpus are siblings within a package (all cpus are
core siblings). This shows performance improvements of up to 10%,
depending on the workload.

In order to keep the current behaviour, but also allow to switch to
the different core sibling topology use the existing "topology="
kernel parameter:

Specifying "topology=on" on machines without topology information will
generate the core siblings (fake) topology information, instead of the
default topology information where all cpus have the maximum distance.

On machines which provide topology information specifying
"topology=on" does not have any effect.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens
2017-09-19 12:52:22 +02:00
committed by Martin Schwidefsky
parent ba385c0594
commit 1b25fda053
2 changed files with 61 additions and 23 deletions
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12
arch/s390/kernel/early.c
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@@ -404,18 +404,6 @@ static inline void save_vector_registers(void)
#endif
}
static int __init topology_setup(char *str)
{
bool enabled;
int rc;
rc = kstrtobool(str, &enabled);
if (!rc && !enabled)
S390_lowcore.machine_flags &= ~MACHINE_FLAG_TOPOLOGY;
return rc;
}
early_param("topology", topology_setup);
static int __init disable_vector_extension(char *str)
{
S390_lowcore.machine_flags &= ~MACHINE_FLAG_VX;