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e8e8a2e47d
linux/drivers/char
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Andi Kleen e8e8a2e47d random: optimize add_interrupt_randomness 
add_interrupt_randomess always wakes up
code blocking on /dev/random. This wake up is done
unconditionally. Unfortunately this means all interrupts
take the wait queue spinlock, which can be rather expensive
on large systems processing lots of interrupts.

We saw 1% cpu time spinning on this on a large macro workload
running on a large system.

I believe it's a recent regression (?)

Always check if there is a waiter on the wait queue
before waking up. This check can be done without
taking a spinlock.

1.06%         10460  [kernel.vmlinux] [k] native_queued_spin_lock_slowpath
         |
         ---native_queued_spin_lock_slowpath
            |
             --0.57%--_raw_spin_lock_irqsave
                       |
                        --0.56%--__wake_up_common_lock
                                  credit_entropy_bits
                                  add_interrupt_randomness
                                  handle_irq_event_percpu
                                  handle_irq_event
                                  handle_edge_irq
                                  handle_irq
                                  do_IRQ
                                  common_interrupt

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2018-02-28 18:01:16 -05:00
..
agp pci-v4.16-changes 2018-02-06 09:59:40 -08:00
hw_random Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-02-14 17:02:15 -08:00
ipmi vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
mwave char/mwave: make some arrays static const to make object code smaller 2017-07-17 17:23:16 +02:00
pcmcia vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
tpm vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
xilinx_hwicap char: xilinx_hwicap: Fix warnings in the driver 2017-08-28 17:04:47 +02:00
xillybus vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
apm-emulation.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
applicom.c applicom: constify pci_device_id. 2017-08-28 17:11:28 +02:00
applicom.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bfin-otp.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
bsr.c
ds1302.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ds1620.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
dsp56k.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
dtlk.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
efirtc.c
generic_nvram.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
hangcheck-timer.c treewide: Switch DEFINE_TIMER callbacks to struct timer_list * 2017-11-21 15:57:05 -08:00
hpet.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
lp.c char: lp: use true or false for boolean values 2018-01-25 10:56:02 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mbcs.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
mbcs.h
mem.c /dev/mem: Add bounce buffer for copy-out 2017-12-18 15:59:17 +01:00
misc.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mspec.c drivers, char: convert vma_data.refcnt from atomic_t to refcount_t 2017-03-23 13:57:19 +01:00
nsc_gpio.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
nvram.c char/nvram: set array of const as const 2016-02-08 14:57:30 -08:00
nwbutton.c treewide: Switch DEFINE_TIMER callbacks to struct timer_list * 2017-11-21 15:57:05 -08:00
nwbutton.h treewide: Switch DEFINE_TIMER callbacks to struct timer_list * 2017-11-21 15:57:05 -08:00
nwflash.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
pc8736x_gpio.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
powernv-op-panel.c powerpc/powernv: Add driver for operator panel on FSP machines 2016-06-29 17:33:46 +10:00
ppdev.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
ps3flash.c wrappers for ->i_mutex access 2016-01-22 18:04:28 -05:00
random.c random: optimize add_interrupt_randomness 2018-02-28 18:01:16 -05:00
raw.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
rtc.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
scx200_gpio.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
snsc_event.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/signal.h> 2017-03-02 08:42:29 +01:00
snsc.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
snsc.h
sonypi.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
tb0219.c mips: separate extable.h, switch module.h to it 2016-10-05 18:36:18 -04:00
tile-srom.c tile-srom: allow the driver to be built as a module 2016-11-10 15:18:56 +01:00
tlclk.c timer: Remove last user of TIMER_INITIALIZER 2017-10-05 15:01:18 +02:00
toshiba.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
ttyprintk.c ttyprintk: Neaten and simplify printing 2016-09-13 17:30:17 +02:00
uv_mmtimer.c
virtio_console.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00