| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Mon, 15 Aug 2011 17:51:57 +0200 From: Frederic Weisbecker <fweisbec@...il.com> To: LKML <linux-kernel@...r.kernel.org> Cc: Frederic Weisbecker <fweisbec@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Anton Blanchard <anton@....ibm.com>, Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>, Lai Jiangshan <laijs@...fujitsu.com>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Paul Menage <menage@...gle.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Stephen Hemminger <shemminger@...tta.com>, Thomas Gleixner <tglx@...utronix.de>, Tim Pepper <lnxninja@...ux.vnet.ibm.com> Subject: [RFC PATCH 00/32] Nohz cpusets (was: Nohz Tasks) So it's still in draft stage. It's far from covering everything the periodic timer does but it has made some progress since last posting. So I think it's time now for another early release. = What's that? = On the mainline kernel we have a feature (CONFIG_NO_HZ) that is able to turn off the periodic scheduler tick when the CPU has nothing to do, namely when it's running the idle task. The scheduler tick handles many things like RCU and scheduler internal state, jiffies accouting, wall time accounting, load accounting, cputime accounting, timer wheel, posix cpu timers, etc... However by the time we run idle and the CPU is going to sleep, none of these things are useful for the CPU. We can then shut it down. The benefit of this is for energy saving purposes. We avoid to wake up the CPU needlessly with these useless interrupts. What this patchset do is to extend that feature to non idle cases, implementing some new kind of "adaptive nohz". But the purpose is different and the implementation too. = How does that work = It tries to handle all the things that the timer tick usually handle but using different tricks. Sometimes we can't really afford to avoid the periodic tick, but sometimes we can and if we do, we need to take some special care. - We can't shutdown the tick if we have more than one task running, due to the need for the tick for preemption. But I believe that one day we can avoid the periodic tick for that and rather anticipate when the scheduler really needs the tick. - We can't shutdown the tick if RCU needs to complete a grace period from the current CPU, or if it has callbacks to handle. - We can't shutdown the tick if we have a posix cpu timer queued. Similarly to the preemption case, we should be able to anticipate that with a precise timer and avoid a periodic check based on HZ. - Restart the tick when more than one non-idle task are in the runqueue. - We need to handle process accounting, RCU, rq clock, task tick, etc... And that patchset for now only handles a part of the whole needs. = What's the interface = We use the cpuset interface by adding a nohz flag to it. As long as a CPU is part of a nohz cpuset, then this CPU will try to enter into adaptive nohz mode when it can, even if it is part of another cpuset that is not nohz. = Why do we need that? = There are at least two potential users of this feature: * High performance computing: To optimize the throughput, some workloads involve running one task per CPU that mostly run in userspace. These tasks don't want and don't need to suffer from the overhead of the timer interrupt. It consumes CPU time and it trashes the CPU cache. * Real time: Minimizing timer interrupts means less interrupts and thus less critical sections that usually induce latency. = What's missing? = Many things like handling of perf events, irq work, sched clock tick, runqueue clock, sched_class::task_tick(), rq clock, cpu load, ... The handling of cputimes is also incomplete as there are other places that use the utime/stime. Process time accounting is globally incomplete. But anyway the thing is moving forward. An early posting was just very needed at that step. For those who want to play: git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git nohz/cpuset-v1 Frederic Weisbecker (32): nohz: Drop useless call in tick_nohz_start_idle() nohz: Drop ts->idle_active nohz: Drop useless ts->inidle check before rearming the tick nohz: Separate idle sleeping time accounting from nohz switching nohz: Move rcu dynticks idle mode handling to idle enter/exit APIs nohz: Move idle ticks stats tracking out of nohz handlers nohz: Rename ts->idle_tick to ts->last_tick nohz: Move nohz load balancer selection into idle logic nohz: Move ts->idle_calls into strict idle logic nohz: Move next idle expiring time record into idle logic area cpuset: Set up interface for nohz flag nohz: Try not to give the timekeeping duty to a cpuset nohz cpu nohz: Adaptive tick stop and restart on nohz cpuset nohz/cpuset: Don't turn off the tick if rcu needs it nohz/cpuset: Restart tick when switching to idle task nohz/cpuset: Wake up adaptive nohz CPU when a timer gets enqueued x86: New cpuset nohz irq vector nohz/cpuset: Don't stop the tick if posix cpu timers are running nohz/cpuset: Restart tick when nohz flag is cleared on cpuset nohz/cpuset: Restart the tick if printk needs it rcu: Restart the tick on non-responding adaptive nohz CPUs rcu: Restart tick if we enqueue a callback in a nohz/cpuset CPU nohz/cpuset: Account user and system times in adaptive nohz mode nohz/cpuset: Handle kernel entry/exit to account cputime nohz/cpuset: New API to flush cputimes on nohz cpusets nohz/cpuset: Flush cputime on threads in nohz cpusets when waiting leader nohz/cpuset: Flush cputimes on procfs stat file read nohz/cpuset: Flush cputimes for getrusage() and times() syscalls x86: Syscall hooks for nohz cpusets x86: Exception hooks for nohz cpusets rcu: Switch to extended quiescent state in userspace from nohz cpuset nohz/cpuset: Disable under some configs arch/Kconfig | 3 + arch/arm/kernel/process.c | 4 +- arch/avr32/kernel/process.c | 4 +- arch/blackfin/kernel/process.c | 4 +- arch/microblaze/kernel/process.c | 4 +- arch/mips/kernel/process.c | 4 +- arch/powerpc/kernel/idle.c | 4 +- arch/powerpc/platforms/iseries/setup.c | 8 +- arch/s390/kernel/process.c | 4 +- arch/sh/kernel/idle.c | 4 +- arch/sparc/kernel/process_64.c | 4 +- arch/tile/kernel/process.c | 4 +- arch/um/kernel/process.c | 4 +- arch/unicore32/kernel/process.c | 4 +- arch/x86/Kconfig | 1 + arch/x86/include/asm/entry_arch.h | 3 + arch/x86/include/asm/hw_irq.h | 6 + arch/x86/include/asm/irq_vectors.h | 2 + arch/x86/include/asm/smp.h | 11 + arch/x86/include/asm/thread_info.h | 10 +- arch/x86/kernel/entry_64.S | 4 + arch/x86/kernel/irqinit.c | 4 + arch/x86/kernel/process_32.c | 4 +- arch/x86/kernel/process_64.c | 5 +- arch/x86/kernel/ptrace.c | 10 + arch/x86/kernel/smp.c | 26 ++ arch/x86/kernel/traps.c | 22 +- arch/x86/mm/fault.c | 13 +- fs/proc/array.c | 2 + include/linux/cpuset.h | 29 ++ include/linux/kernel_stat.h | 2 + include/linux/posix-timers.h | 1 + include/linux/rcupdate.h | 1 + include/linux/sched.h | 10 +- include/linux/tick.h | 50 +++- init/Kconfig | 8 + kernel/cpuset.c | 105 +++++++ kernel/exit.c | 2 + kernel/posix-cpu-timers.c | 12 + kernel/printk.c | 17 +- kernel/rcutree.c | 28 ++- kernel/sched.c | 132 +++++++++- kernel/softirq.c | 6 +- kernel/sys.c | 6 + kernel/time/tick-sched.c | 479 ++++++++++++++++++++++++-------- kernel/time/timer_list.c | 4 +- kernel/timer.c | 8 +- 47 files changed, 897 insertions(+), 185 deletions(-) -- 1.7.5.4 -- 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/
Powered by blists - more mailing lists