update smp related documentation after recent changes
Remove references to machdep.hlt_logical_cpus and machdep.hlt_cpus sysctls and tunables. Document machdep.hyperthreading_allowed and hint.lapic.X.disabled tunables. Prompted by: ru Proofreading: bf Reviewed by: jhb Approved by: re (kib)
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2020-12-20 02:59:44 +00:00
svn path=/head/; revision=224528
@ -196,10 +196,8 @@
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Because this naive scheduling can result in suboptimal
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performance, under certain circumstances it may be useful to
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disable the logical processors with the the
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<varname>machdep.hlt_logical_cpus</varname> sysctl variable.
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It is also possible to halt any CPU in the idle loop with the
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<varname>machdep.hlt_cpus</varname> sysctl variable. The
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&man.smp.4; manual page has more details.</para>
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<varname>machdep.hyperthreading_allowed</varname> tunable.
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The &man.smp.4; manual page has more details.</para>
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<para>&os; will take advantage of Physical Address Extensions
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(PAE) support on CPUs that support this feature. A kernel
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@ -63,10 +63,10 @@ the read-only sysctl variable
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.Pp
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.Fx
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allows specific CPUs on a multi-processor system to be disabled.
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The sysctl variable
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.Va machdep.hlt_cpus
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is an integer bitmask denoting CPUs to halt, counting from 0.
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Setting a bit to 1 will result in the corresponding CPU being
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This can be done using the
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.Va hint.lapic.X.disabled
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tunable, where X is the APIC ID of a CPU.
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Setting this tunable to 1 will result in the corresponding CPU being
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disabled.
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.Pp
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The
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@ -122,12 +122,12 @@ tasks on CPUs that are closely grouped together.
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supports hyperthreading on Intel CPU's on the i386 and AMD64 platforms.
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Since using logical CPUs can cause performance penalties under certain loads,
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the logical CPUs can be disabled by setting the
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.Va machdep.hlt_logical_cpus
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sysctl to one.
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Note that this operation is different from the mechanism used by the
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.Va machdep.hyperthreading_allowed
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tunable to zero.
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.Xr cpuset 1 .
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.Sh SEE ALSO
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.Xr mptable 1 ,
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.Xr loader 8 ,
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.Xr sysctl 8 ,
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.Xr condvar 9 ,
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.Xr msleep 9 ,
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@ -1233,24 +1233,12 @@ machdep.disable_mtrrs
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machdep.guessed_bootdev
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---
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machdep.hlt_cpus
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machdep.hyperthreading_allowed
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bool
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This option will permit the halting
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of CPUs.
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For instance, to halt CPU 0,
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machdep.htl_cpus=1 can be used.
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It is possible to halt two CPUs by providing
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a comma separated list (i.e: cpu1,cpu2).
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---
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machdep.hlt_logical_cpus
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bool
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This keeps the logical CPUs halted in the idle loop.
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By default the logical CPUs are halted at startup.
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It is also possible to halt any cpu in the idle loop now
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using machdep.hlt_cpus.
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Setting this tunable to zero disables
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the use of additional logical processors
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provided by Intel HTT technology.
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---
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machdep.panic_on_nmi
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