Bart Smaalders wrote:
Haris wrote:
Today Solaris uses per-process TSBs, so walking a TSB
to clear
out entries for a stolen context is never necessary.
In addition,
e now use grouped assignment of mmu contexts; this
means that
if a context needs to be stolen we only need to
cross-call
other cpus in its mmu context domain instead of every
cpu in the box.
Take a look here for details:
http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/
usr/src/uts/sfmmu/vm/hat_sfmmu.h#289
What about the TLB? TLB still has entries from multiple contexts, right?
Yes.
I was looking at the code you pointed me and I have a question about
the mmu context domain. What is meant by MMU context domain? The
subset of CPUs that have entries for a context space?
The idea is that a set of cpus can have the same idea of
addresss space -> mmu context id mappings. Thus, when stealing
a mmu context, only the set of CPUs in the mmu context domain need
to receive cross-calls.
Note that on threaded processors, virtual cpus on the
same core (threads) share the same TLB:
From
http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/sfmmu/vm/hat_sfmmu.c#1370:
/*
* plat_cpuid_to_mmu_ctx_info() is a platform interface that returns MMU
* context domain information for a given CPU. If a platform does not
* specify that interface, then the function below is used instead to
return
* default information. The defaults are as follows:
*
* - For sun4u systems there's one MMU context domain per CPU.
* This default is used by all sun4u systems except OPL. OPL systems
* provide platform specific interface to map CPU ids to MMU ids
* because on OPL more than 1 CPU shares a single MMU.
* Note that on sun4v, there is one global context domain for
* the entire system. This is to avoid running into potential problem
* with ldom physical cpu substitution feature.
* - The number of MMU context IDs supported on any CPU in the
* system is 8K.
*/
- Bart
So, when creating a new process, is it possible that the address space
get mapped to different context IDs for different MMUs?
Les say we have the case of sun4u (different MMU for each CPU). My guess
is that when you create a new process with threads less than the number
of physical cpus the address space is mapped to some context IDs at that
time; possibly the same context ID in case of not wraparound. But if
later a thread of a process migrates to a CPU that no other thread of
that process was scheduled before, it is possible that for that
processor the address space may be mapped to a different context ID.
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