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SubjectRe: [ANNOUNCE] 3.7-nohz1
Hi,

On Thu, Dec 20, 2012 at 11:32 AM, Frederic Weisbecker
<fweisbec@gmail.com> wrote:
> Hi,
>
> So this is a new version of the nohz cpusets based on 3.7, except it's not using
> cpusets anymore and I actually based it on the middle of the 3.8 merge window
> in order to get latest upstream full dynticks preparatory work: cputime cleanups,
> RCU user mode, context tracking subsystem, nohz code consolidation, ...
>
> So the big changes since the last nohz cpuset release are:
>
> * printk now uses irq work so it doesn't rely on the tick anymore (provided
> your arch implements irq work with IPIs or alike). This chunk has been proposed
> for the 3.8 merge window: https://lkml.org/lkml/2012/12/17/177
> May be Linus will pull, may be not. We'll see. In any case I've included it in this tree
> but I'm not reposting this part of the patchset to avoid spamming you.
>
> * cputime doesn't rely on IPIs anymore. Now the reader does a special computation to
> remotely get the tickless cputime.
>
> * No more cpusets interface. Paul McKenney suggested me to start with a boot time
> kernel parameter to define the full dynticks cpumask. And he was totally right, it
> makes the code much more simple. That's a good way to start and to make the mainlining
> easier. We can still add a runtime configuration later if necessary.

It would be nice to have the runtime configuration ability. A percpu control
file such as /sys/devices/system/cpu/cpuX/isol could configure that cpu with
different levels of isolation. Users could echo bitmasks where each bit is
associated with a level of isolation. echo 0 disables all isolation.
Bit 1 disables
RCU callbacks on that CPU, bit 2 isolates the CPU from the general scheduler
just like isolcpus boot argument does, bit 3 pushes all irqs away, bit 4 turns
off the ticks etc.

I always hoped that someone will make isolcpus a runtime option so I guess
it is time to get my hands dirty. Any pointers for this?

>
> * Now there is always a CPU handling the timekeeping. This can be further optimized
> and more power-friendly, I really did something simple-stupid. I guess we'll try to get
> that into a better shape with Hakan. But at least the timekeeping now works.

Will look into it.

>
> * It uses the new RCU callbacks offlining feature. This way a full dynticks CPU doesn't
> need to keep the tick to handle local callbacks. This is still very experimental though.
>
> * No more specific IPI vector for full dynticks. We just use the scheduler ipi.
>
> The branch is:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 3.7-nohz1
>
> There is still quite some work to do.
>
> == How to use? ==
>
> Select:
> CONFIG_NO_HZ
> CONFIG_RCU_USER_QS
> CONFIG_VIRT_CPU_ACCOUNTING_GEN
> CONFIG_RCU_NOCB_CPU
> CONFIG_NO_HZ_FULL
>
> You always need at least one timekeeping CPU.
>
> Let's imagine you have 4 CPUs. We keep the CPU 0 to offline RCU callbacks there and to
> handle the timekeeping. We set the rest as full dynticks. So you need the following kernel
> parameters:
>
> rcu_nocbs=1-3 full_nohz=1-3
>
> (Note rcu_nocbs value must always be the same as full_nohz).
>
> Now if you want proper isolation you need to:
>
> * Migrate your processes adequately
> * Migrate your irqs to CPU 0
> * Migrate the RCU nocb threads to CPU 0. Example with the above configuration:
>
> for p in $(ps -o pid= -C rcuo1,rcuo2,rcuo3)
> do
> taskset -cp 0 $p
> done
>
> Then run what you want on the full dynticks CPUs. For best results, run 1 task
> per CPU, mostly in userspace and mostly CPU bound (otherwise more IO = more kernel
> mode execution = more chances to get IPIs, tick restarted, workqueues, kthreads, etc...)
>
> This page contains a good reminder for those interested in CPU isolation: https://github.com/gby/linux/wiki
>
> But keep in mind that my tree is not yet ready for serious production.
>
> Happy Christmas, new year or whatever end of the world.
> ---
>
> Frederic Weisbecker (32):
> irq_work: Fix racy IRQ_WORK_BUSY flag setting
> irq_work: Fix racy check on work pending flag
> irq_work: Remove CONFIG_HAVE_IRQ_WORK
> nohz: Add API to check tick state
> irq_work: Don't stop the tick with pending works
> irq_work: Make self-IPIs optable
> printk: Wake up klogd using irq_work
> Merge branch 'nohz/printk-v8' into 3.7-nohz1-stage
> context_tracking: Add comments on interface and internals
> cputime: Generic on-demand virtual cputime accounting
> cputime: Allow dynamic switch between tick/virtual based cputime accounting
> cputime: Use accessors to read task cputime stats
> cputime: Safely read cputime of full dynticks CPUs
> nohz: Basic full dynticks interface
> nohz: Assign timekeeping duty to a non-full-nohz CPU
> nohz: Trace timekeeping update
> nohz: Wake up full dynticks CPUs when a timer gets enqueued
> rcu: Restart the tick on non-responding full dynticks CPUs
> sched: Comment on rq->clock correctness in ttwu_do_wakeup() in nohz
> sched: Update rq clock on nohz CPU before migrating tasks
> sched: Update rq clock on nohz CPU before setting fair group shares
> sched: Update rq clock on tickless CPUs before calling check_preempt_curr()
> sched: Update rq clock earlier in unthrottle_cfs_rq
> sched: Update clock of nohz busiest rq before balancing
> sched: Update rq clock before idle balancing
> sched: Update nohz rq clock before searching busiest group on load balancing
> nohz: Move nohz load balancer selection into idle logic
> nohz: Full dynticks mode
> nohz: Only stop the tick on RCU nocb CPUs
> nohz: Don't turn off the tick if rcu needs it
> nohz: Don't stop the tick if posix cpu timers are running
> nohz: Add some tracing
>
> Steven Rostedt (2):
> irq_work: Flush work on CPU_DYING
> irq_work: Warn if there's still work on cpu_down
>
> arch/alpha/Kconfig | 1 -
> arch/alpha/kernel/osf_sys.c | 6 +-
> arch/arm/Kconfig | 1 -
> arch/arm64/Kconfig | 1 -
> arch/blackfin/Kconfig | 1 -
> arch/frv/Kconfig | 1 -
> arch/hexagon/Kconfig | 1 -
> arch/mips/Kconfig | 1 -
> arch/parisc/Kconfig | 1 -
> arch/powerpc/Kconfig | 1 -
> arch/s390/Kconfig | 1 -
> arch/s390/kernel/vtime.c | 4 +-
> arch/sh/Kconfig | 1 -
> arch/sparc/Kconfig | 1 -
> arch/x86/Kconfig | 1 -
> arch/x86/kernel/apm_32.c | 11 +-
> drivers/isdn/mISDN/stack.c | 7 +-
> drivers/staging/iio/trigger/Kconfig | 1 -
> fs/binfmt_elf.c | 8 +-
> fs/binfmt_elf_fdpic.c | 7 +-
> include/asm-generic/cputime.h | 1 +
> include/linux/context_tracking.h | 28 +++++
> include/linux/hardirq.h | 4 +-
> include/linux/init_task.h | 9 ++
> include/linux/irq_work.h | 20 +++
> include/linux/kernel_stat.h | 2 +-
> include/linux/posix-timers.h | 1 +
> include/linux/printk.h | 3 -
> include/linux/rcupdate.h | 8 ++
> include/linux/sched.h | 48 +++++++-
> include/linux/tick.h | 26 ++++-
> include/linux/vtime.h | 47 +++++---
> init/Kconfig | 22 +++-
> kernel/acct.c | 6 +-
> kernel/context_tracking.c | 91 +++++++++++----
> kernel/cpu.c | 4 +-
> kernel/delayacct.c | 7 +-
> kernel/exit.c | 6 +-
> kernel/fork.c | 8 +-
> kernel/irq_work.c | 131 ++++++++++++++++-----
> kernel/posix-cpu-timers.c | 39 +++++-
> kernel/printk.c | 36 +++---
> kernel/rcutree.c | 19 +++-
> kernel/rcutree_plugin.h | 13 +--
> kernel/sched/core.c | 69 +++++++++++-
> kernel/sched/cputime.c | 222 ++++++++++++++++++++++++++++++-----
> kernel/sched/fair.c | 42 +++++++-
> kernel/sched/sched.h | 15 +++
> kernel/signal.c | 12 ++-
> kernel/softirq.c | 11 +-
> kernel/time/Kconfig | 9 ++
> kernel/time/tick-broadcast.c | 3 +-
> kernel/time/tick-common.c | 5 +-
> kernel/time/tick-sched.c | 142 ++++++++++++++++++++---
> kernel/timer.c | 3 +-
> kernel/tsacct.c | 19 ++-
> 56 files changed, 955 insertions(+), 233 deletions(-)


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