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Date: Wed, 11 Dec 2013 20:06:36 -0500 From: Paul Gortmaker <paul.gortmaker@...driver.com> To: Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> CC: Andrew Morton <akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>, Paul Gortmaker <paul.gortmaker@...driver.com> Subject: [PATCH 0/3] Introduce simple wait queues The simple wait queue support has existed for quite some time (at least since 3.4) in the preempt-rt kernels. At this years RT summit, we agreed that it makes sense to do the final cleanups on it and aim to mainline it. It is similar to normal waitqueue support, but without some of the less used functionality, giving it a smaller footprint vs. the normal wait queue. For non-RT, we can still benefit from the footprint reduction factor. Here in this series, we deploy the simple wait queues in two places: (1) for completions, and (2) in RCU processing. As can be seen below from the bloat meter, we still come out ahead even after adding the new swait code. Plus there are other deployment places pending, for additional benefits. Thomas originally created it in order to avoid issues with the waitqueue head lock on RT, as it can't be converted to a raw lock, which in turn limits the contexts from which you can manipulate wait queues. The simple wait queue head uses a raw lock and hence queue manipulations can be done while atomic. Output from: ./scripts/bloat-o-meter ../simplewait-absent/vmlinux ../simplewait-present/vmlinux ----------------------------------------------------------------------------------- add/remove: 15/0 grow/shrink: 3/46 up/down: 821/-822 (-1) function old new delta __swake_up_locked - 156 +156 swait_prepare - 112 +112 __swake_up - 88 +88 swait_finish - 83 +83 rcu_nocb_kthread 718 793 +75 swait_prepare_locked - 61 +61 swait_finish_locked - 55 +55 nfs_file_direct_read 665 693 +28 __kstrtab___init_swaitqueue_head - 23 +23 __init_swaitqueue_head - 23 +23 __ksymtab_swait_prepare - 16 +16 __ksymtab_swait_finish - 16 +16 __ksymtab___swake_up - 16 +16 __ksymtab___init_swaitqueue_head - 16 +16 vermagic 27 42 +15 __kstrtab_swait_prepare - 14 +14 __kstrtab_swait_finish - 13 +13 __kstrtab___swake_up - 11 +11 rsp_wakeup 30 28 -2 rcu_report_qs_rnp 287 285 -2 __call_rcu_nocb_enqueue 181 179 -2 wait_rcu_gp 76 69 -7 submit_bio_wait 103 96 -7 nfs_file_direct_write 721 714 -7 kobj_completion_init 59 52 -7 init_pcmcia_cs 61 54 -7 i8042_probe 1602 1595 -7 i2c_del_adapter 610 603 -7 hpet_cpuhp_notify 273 266 -7 flush_kthread_worker 112 105 -7 flow_cache_flush 346 339 -7 ext4_init_fs 631 624 -7 ext4_fill_super 11746 11739 -7 drop_sysctl_table 184 177 -7 device_pm_sleep_init 105 98 -7 crypto_larval_alloc 155 148 -7 autofs4_expire_indirect 1024 1017 -7 autofs4_expire_direct 253 246 -7 ata_port_alloc 431 424 -7 usb_start_wait_urb 324 316 -8 loop_switch.isra 151 143 -8 devtmpfs_delete_node 191 183 -8 cpuidle_add_sysfs 191 183 -8 cpuidle_add_device_sysfs 402 394 -8 cache_wait_req.isra 315 307 -8 devtmpfs_create_node 275 264 -11 kthread 227 213 -14 usb_stor_probe1 1746 1730 -16 usb_sg_init 753 737 -16 scsi_complete_async_scans 320 304 -16 flush_kthread_work 277 261 -16 do_fork 766 750 -16 do_coredump 3540 3524 -16 _rcu_barrier 632 616 -16 rcu_init_one 1069 1040 -29 rcu_gp_kthread 1578 1538 -40 wait_for_completion_timeout 261 213 -48 wait_for_completion_io_timeout 261 213 -48 wait_for_completion_io 248 200 -48 wait_for_completion 248 200 -48 wait_for_completion_interruptible_timeout 286 235 -51 wait_for_completion_killable_timeout 316 253 -63 wait_for_completion_killable 349 286 -63 wait_for_completion_interruptible 335 268 -67 Two notes with respect to bloat: 1) vermagic being larger is just noise; vanilla is v3.13-rc3 and swait is 3.13.0-rc3-00003-ga0388b5 because I had LOCALVERSION_AUTO enabled. 2) The nfs_file_direct_read increase appears to be the butterfly effect causing gcc to do some rethinking of how it optimizes things; disassembly showed different register choices here and there, but no big obvious change such as inline-ing a function or similar. (gcc-4.8.1) Testing: -------- Comparison of v3.13-r3-vanilla vs. v3.13-r3-simplewait, RCU configured as: CONFIG_TREE_RCU=y CONFIG_RCU_STALL_COMMON=y CONFIG_RCU_USER_QS=y CONFIG_RCU_FANOUT=64 CONFIG_RCU_FANOUT_LEAF=16 CONFIG_RCU_FAST_NO_HZ=y CONFIG_RCU_NOCB_CPU=y CONFIG_RCU_NOCB_CPU_ALL=y Timing defconfig build of v3.13-rc3, with rcu's offloaded to core zero (for i in `pgrep rcuo` ; do taskset -c -p 0 $i ; done) and build run on 1-7 (single socket quad hyperthread dell 990) # make clean ; make defconfig ; reboot, ssh in... git status sync time taskset -c 1-7 make -j20 > /dev/null Do above run three times each to gauge consistency. v3.13-r3-vanilla ---------------- real 2m19.486s user 13m7.091s sys 0m47.647s real 2m19.061s user 13m10.232s sys 0m47.846s real 2m18.864s user 13m8.623s sys 0m47.942s v3.13-r3-simplewait ------------------- real 2m19.271s user 13m7.845s sys 0m48.028s real 2m18.374s user 13m9.828s sys 0m48.084s real 2m18.344s user 13m8.528s sys 0m48.014s So in this particular test, it looks like the change is lost in the noise. At least there isn't any blatant regressions. A rcutorture run has been going for 2 1/2 hrs so far and hasn't spit out any failure type messages so far... Changes vs. the 3.10-rt patches it was based on: ------------------------------------------------ Warning: Not probably interesting to anyone other than RT folks who have played with the previous versions of the patches. -prior to 3.13, some of the wait and completion code was still in sched/core.c so I've had to relocate accordingly. -the -rt adapt to completion patch did some renaming of the simple wait boilerplate; that has been pushed back down into the simplewait introductory commit. -where possible, I've aligned the names of the simple wait functions to be just the normal wait functions, but with the added "s" prefix. This makes review easier, and avoids bugs like we had in -rt where, swake_up was confused as a replacement for wake_all In -rt this was a separate patch from me; it is now squashed into the simplewait introductory commit as well. -in -rt the file was include/wait-simple.h ; here I've used swait.h since it is more in alignment with the function names used above. -in RT, there were two tracing_off() additions based on the value of migrate_disable_atomic, but the latter is RT specific, so drop those two chunks for this mainline version. -in the -rt, we will still need PeterZ's follow on patch to ensure we don't call an unlimited number of ttwu with a raw lock held, but for now, I'd rather keep that as -rt specific; hoping we can find a better solution..? http://marc.info/?l=linux-kernel&m=138089860308430&w=2 Paul. --- Thomas Gleixner (3): wait-simple: Introduce the simple waitqueue implementation sched/core: convert completions to use simple wait queues rcu: use simple wait queues where possible in rcutree include/linux/completion.h | 8 +- include/linux/swait.h | 220 +++++++++++++++++++++++++++++++++++++++++++++ include/linux/uprobes.h | 1 + kernel/Makefile | 2 +- kernel/rcu/tree.c | 16 ++-- kernel/rcu/tree.h | 7 +- kernel/rcu/tree_plugin.h | 14 +-- kernel/sched/completion.c | 34 +++---- kernel/swait.c | 118 ++++++++++++++++++++++++ 9 files changed, 380 insertions(+), 40 deletions(-) create mode 100644 include/linux/swait.h create mode 100644 kernel/swait.c -- 1.8.5.1 -- 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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