Rafi Gordon wrote:
I have ran ps aux |grep migration on 2 machines,
one with FC4 on x86 (NON smp kernel) and one on FC4 on x86_64
(SMP kernel).
Each of these machines has a single CPU.
On the first (x86) machine, there was no result.
On the second (x86_64) there were 2 instances of the migration
thread.
What does this say? Is it had to do with
hyperthreading ? I doubt it.
It says that on the SMP kernel your OS two "virtual cores" (a name I
just invented to describe how the OS see's two CPU's although there is
only one with hyperthreading) and therefore it fired up a migration
kernel thread for each CPU it sees.
If I remember well , you can know if an Intel x86/x86_64 processor
supports hyperthreading by looking at the flags in /proc/cpu ;
if "ht" exists, it supports hyperthreading (Though I am not
fully shure in this point).
And both these machines had the "ht" flags in /proc/cpuinfo.
Without an SMP kernel hyperthreading is practicly turned off.
Is it has to do with the fact that one machine ran
NON-smp kernel and had zero migration threads while
the other machine ran SMP kernel and had 2 migration threads?
Yes, the machine with the SMP kernel can "see" and operate that two
"virtual cores" of the hyperthreaded CPU. Without SMP support, they cannot.
Will I have 2 migration threads if I will install an
SMP kernel on the x86 machine ?
Yes.
What does this migration thread do, in short?
Load balance tasks between CPU's. The scheduler prefers to give each the
same CPU for each of it's runs to make the best use of various caches.
It is the job of the migratiopn threads to consider the possability that
a task will be better served on a different CPU and "migrate" it there.
Gilad
--
Gilad Ben-Yossef <[EMAIL PROTECTED]>
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