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Date: Thu, 20 Dec 2012 22:20:13 -0700 From: Hakan Akkan <hakanakkan@...il.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, Alessio Igor Bogani <abogani@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Avi Kivity <avi@...hat.com>, Chris Metcalf <cmetcalf@...era.com>, Christoph Lameter <cl@...ux.com>, Geoff Levand <geoff@...radead.org>, Gilad Ben Yossef <gilad@...yossef.com>, Ingo Molnar <mingo@...nel.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Paul Gortmaker <paul.gortmaker@...driver.com>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>, Li Zhong <zhong@...ux.vnet.ibm.com> Subject: Re: [ANNOUNCE] 3.7-nohz1 Hi, On Thu, Dec 20, 2012 at 11:32 AM, Frederic Weisbecker <fweisbec@...il.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(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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