Linus, please pull CPU isolation extensions from
git://git.kernel.org/pub/scm/linux/kernel/git/maxk/cpuisol-2.6.git for-linus
Diffstat:
b/arch/x86/Kconfig | 1
b/arch/x86/kernel/genapic_flat_64.c | 5 ++-
b/drivers/base/cpu.c | 48 +++++++++++++++++++++++++++++++++++
b/include/linux/cpumask.h | 3 ++
b/kernel/Kconfig.cpuisol | 15 +++++++++++
b/kernel/Makefile | 4 +-
b/kernel/cpu.c | 49 ++++++++++++++++++++++++++++++++++++
b/kernel/sched.c | 37 ---------------------------
b/kernel/stop_machine.c | 9 +++++-
b/kernel/workqueue.c | 31 ++++++++++++++++------
kernel/Kconfig.cpuisol | 26 ++++++++++++++++++-
11 files changed, 176 insertions(+), 52 deletions(-)
The patchset consist of 4 patches.
cpuisol: Make cpu isolation configrable and export isolated map
cpuisol: Do not route IRQs to the CPUs isolated at boot
cpuisol: Do not schedule workqueues on the isolated CPUs
cpuisol: Do not halt isolated CPUs with Stop Machine
First two are very simple. They simply make "CPU isolation" a
configurable feature, export cpu_isolated_map and provide some helper functions
to access it (just
like cpu_online() and friends).
Last two patches add support for isolating CPUs from running workqueus and stop
machine. Last patch
is kind of controversial let me know if you think it's too ugly and I'll resend
without it.
For more details see below.
----
This patch series extends CPU isolation support. Yes, most people want to
virtuallize
CPUs these days and I want to isolate them :) .
The primary idea here is to be able to use some CPU cores as the dedicated
engines for running
user-space code with minimal kernel overhead/intervention, think of it as an
SPE in the
Cell processor. I'd like to be able to run a CPU intensive (%100) RT task on
one of the
processors without adversely affecting or being affected by the other system
activities.
System activities here include _kernel_ activities as well.
I'm personally using this for hard realtime purposes. With CPU isolation it's
very easy to
achieve single digit usec worst case and around 200 nsec average response times
on off-the-shelf
multi- processor/core systems (vanilla kernel plus these patches) even under
exteme system load.
I'm working with legal folks on releasing hard RT user-space framework for that.
I believe with the current multi-core CPU trend we will see more and more
applications that
explore this capability: RT gaming engines, simulators, hard RT apps, etc.
Hence the proposal is to extend current CPU isolation feature.
The new definition of the CPU isolation would be:
---
1. Isolated CPU(s) must not be subject to scheduler load balancing
Users must explicitly bind threads in order to run on those CPU(s).
2. By default interrupts must not be routed to the isolated CPU(s)
User must route interrupts (if any) to those CPUs explicitly.
3. In general kernel subsystems must avoid activity on the isolated CPU(s) as
much as possible
Includes workqueues, per CPU threads, etc.
This feature is configurable and is disabled by default.
---
I've been maintaining this stuff since around 2.6.18 and it's been running in
production
environment for a couple of years now. It's been tested on all kinds of
machines, from NUMA
boxes like HP xw9300/9400 to tiny uTCA boards like Mercury AXA110.
The messiest part used to be SLAB garbage collector changes. With the new SLUB
all that mess
goes away (ie no changes necessary). Also CFS seems to handle CPU hotplug much
better than O(1)
did (ie domains are recomputed dynamically) so that isolation can be done at
any time (via sysfs).
So this seems like a good time to merge.
We've had scheduler support for CPU isolation ever since O(1) scheduler went
it. In other words
#1 is already supported. These patches do not change/affect that functionality
in any way.
#2 is trivial one liner change to the IRQ init code.
#3 is addressed by a couple of separate patches. The main problem here is that
RT thread can prevent
kernel threads from running and machine gets stuck because other CPUs are
waiting for those threads
to run and report back.
Folks involved in the scheduler/cpuset development provided a lot of feedback
on the first series
of patches. I believe I managed to explain and clarify every aspect.
Paul Jackson initially suggested to implement #2 and #3 using cpusets
subsystem. Paul and I looked
at it more closely and determined that exporting cpu_isolated_map instead is a
better option.
Last patch to the stop machine is potentially unsafe and is marked as highly
experimental. Unfortunately
it's currently the only option that allows dynamic module insertion/removal for
above scenarios.
If people still feel that it's toooo ugly I can revert that change and keep it
in the separate tree
for now.
Thanx
Max
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
