linux/include/asm-x86_64
Jakub Jelinek 4732efbeb9 [PATCH] FUTEX_WAKE_OP: pthread_cond_signal() speedup
ATM pthread_cond_signal is unnecessarily slow, because it wakes one waiter
(which at least on UP usually means an immediate context switch to one of
the waiter threads).  This waiter wakes up and after a few instructions it
attempts to acquire the cv internal lock, but that lock is still held by
the thread calling pthread_cond_signal.  So it goes to sleep and eventually
the signalling thread is scheduled in, unlocks the internal lock and wakes
the waiter again.

Now, before 2003-09-21 NPTL was using FUTEX_REQUEUE in pthread_cond_signal
to avoid this performance issue, but it was removed when locks were
redesigned to the 3 state scheme (unlocked, locked uncontended, locked
contended).

Following scenario shows why simply using FUTEX_REQUEUE in
pthread_cond_signal together with using lll_mutex_unlock_force in place of
lll_mutex_unlock is not enough and probably why it has been disabled at
that time:

The number is value in cv->__data.__lock.
        thr1            thr2            thr3
0       pthread_cond_wait
1       lll_mutex_lock (cv->__data.__lock)
0       lll_mutex_unlock (cv->__data.__lock)
0       lll_futex_wait (&cv->__data.__futex, futexval)
0                       pthread_cond_signal
1                       lll_mutex_lock (cv->__data.__lock)
1                                       pthread_cond_signal
2                                       lll_mutex_lock (cv->__data.__lock)
2                                         lll_futex_wait (&cv->__data.__lock, 2)
2                       lll_futex_requeue (&cv->__data.__futex, 0, 1, &cv->__data.__lock)
                          # FUTEX_REQUEUE, not FUTEX_CMP_REQUEUE
2                       lll_mutex_unlock_force (cv->__data.__lock)
0                         cv->__data.__lock = 0
0                         lll_futex_wake (&cv->__data.__lock, 1)
1       lll_mutex_lock (cv->__data.__lock)
0       lll_mutex_unlock (cv->__data.__lock)
          # Here, lll_mutex_unlock doesn't know there are threads waiting
          # on the internal cv's lock

Now, I believe it is possible to use FUTEX_REQUEUE in pthread_cond_signal,
but it will cost us not one, but 2 extra syscalls and, what's worse, one of
these extra syscalls will be done for every single waiting loop in
pthread_cond_*wait.

We would need to use lll_mutex_unlock_force in pthread_cond_signal after
requeue and lll_mutex_cond_lock in pthread_cond_*wait after lll_futex_wait.

Another alternative is to do the unlocking pthread_cond_signal needs to do
(the lock can't be unlocked before lll_futex_wake, as that is racy) in the
kernel.

I have implemented both variants, futex-requeue-glibc.patch is the first
one and futex-wake_op{,-glibc}.patch is the unlocking inside of the kernel.
 The kernel interface allows userland to specify how exactly an unlocking
operation should look like (some atomic arithmetic operation with optional
constant argument and comparison of the previous futex value with another
constant).

It has been implemented just for ppc*, x86_64 and i?86, for other
architectures I'm including just a stub header which can be used as a
starting point by maintainers to write support for their arches and ATM
will just return -ENOSYS for FUTEX_WAKE_OP.  The requeue patch has been
(lightly) tested just on x86_64, the wake_op patch on ppc64 kernel running
32-bit and 64-bit NPTL and x86_64 kernel running 32-bit and 64-bit NPTL.

With the following benchmark on UP x86-64 I get:

for i in nptl-orig nptl-requeue nptl-wake_op; do echo time elf/ld.so --library-path .:$i /tmp/bench; \
for j in 1 2; do echo ( time elf/ld.so --library-path .:$i /tmp/bench ) 2>&1; done; done
time elf/ld.so --library-path .:nptl-orig /tmp/bench
real 0m0.655s user 0m0.253s sys 0m0.403s
real 0m0.657s user 0m0.269s sys 0m0.388s
time elf/ld.so --library-path .:nptl-requeue /tmp/bench
real 0m0.496s user 0m0.225s sys 0m0.271s
real 0m0.531s user 0m0.242s sys 0m0.288s
time elf/ld.so --library-path .:nptl-wake_op /tmp/bench
real 0m0.380s user 0m0.176s sys 0m0.204s
real 0m0.382s user 0m0.175s sys 0m0.207s

The benchmark is at:
http://sourceware.org/ml/libc-alpha/2005-03/txt00001.txt
Older futex-requeue-glibc.patch version is at:
http://sourceware.org/ml/libc-alpha/2005-03/txt00002.txt
Older futex-wake_op-glibc.patch version is at:
http://sourceware.org/ml/libc-alpha/2005-03/txt00003.txt
Will post a new version (just x86-64 fixes so that the patch
applies against pthread_cond_signal.S) to libc-hacker ml soon.

Attached is the kernel FUTEX_WAKE_OP patch as well as a simple-minded
testcase that will not test the atomicity of the operation, but at least
check if the threads that should have been woken up are woken up and
whether the arithmetic operation in the kernel gave the expected results.

Acked-by: Ingo Molnar <mingo@redhat.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Jamie Lokier <jamie@shareable.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Yoichi Yuasa <yuasa@hh.iij4u.or.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-09-07 16:57:17 -07:00
..
8253pit.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
a.out.h [PATCH] x86_64: TASK_SIZE fixes for compatibility mode processes 2005-06-21 18:46:12 -07:00
acpi.h [ACPI] enable C2 and C3 idle power states on SMP 2005-07-12 00:14:36 -04:00
agp.h [PATCH] AGP fix for Xen VMM 2005-06-07 12:35:43 -07:00
apic.h [PATCH] kexec: x86_64: restore apic virtual wire mode on shutdown 2005-06-25 16:24:47 -07:00
apicdef.h [PATCH] kexec: x86: rename APIC_MODE_EXINT 2005-06-25 16:24:46 -07:00
atomic.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
bitops.h [PATCH] x86_64: Fix gcc 4 warning in sched_find_first_bit 2005-07-28 21:46:02 -07:00
boot.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
bootsetup.h [PATCH] Increase number of e820 entries hard limit from 32 to 128 2005-05-01 08:58:51 -07:00
bug.h [PATCH] x86_64: Turn BUG data into valid instruction 2005-07-28 21:46:01 -07:00
bugs.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
byteorder.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
cache.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
cacheflush.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
calling.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
checksum.h [NET]: Fix ipl=>ihl typo in ip_fast_csum 2005-08-29 16:02:48 -07:00
compat.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
cpu.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
cpufeature.h [PATCH] CPUID bug and inconsistency fix 2005-05-01 08:58:49 -07:00
cputime.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
current.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
debugreg.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
delay.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
desc.h [PATCH] x86_64: Some cleanup in setup64.c 2005-07-28 21:45:58 -07:00
div64.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
dma-mapping.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
dma.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
dwarf2.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
e820.h [PATCH] x86_64: Tell VM about holes in nodes 2005-08-26 19:37:12 -07:00
elf.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
emergency-restart.h [PATCH] x86_64: Implemenent machine_emergency_restart 2005-07-26 14:35:42 -07:00
errno.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
fcntl.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
fixmap.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
floppy.h [PATCH] make some things static 2005-05-05 16:36:47 -07:00
fpu32.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
futex.h [PATCH] FUTEX_WAKE_OP: pthread_cond_signal() speedup 2005-09-07 16:57:17 -07:00
genapic.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
hardirq.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
hdreg.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
hpet.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
hw_irq.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
i387.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
ia32.h [PATCH] compat: introduce compat_time_t 2005-06-23 09:45:32 -07:00
ia32_unistd.h [PATCH] inotify: add x86-64 syscall entries 2005-07-26 13:37:22 -07:00
ide.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
io.h [PATCH] reorganize x86-64 NUMA and DISCONTIGMEM config options 2005-06-23 09:45:06 -07:00
io_apic.h [PATCH] x86: i8253/i8259A lock cleanup 2005-06-30 08:45:10 -07:00
ioctl.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
ioctls.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
ipcbuf.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
ipi.h [PATCH] x86_64: Use for_each_cpu_mask for clustered IPI flush 2005-07-28 21:45:57 -07:00
irq.h [PATCH] x86_64: Switch to the interrupt stack when running a softirq in local_bh_enable() 2005-07-28 21:46:02 -07:00
kdebug.h [PATCH] RCU: clean up a few remaining synchronize_kernel() calls 2005-06-25 16:24:38 -07:00
kexec.h [PATCH] Kdump: Export crash notes section address through sysfs 2005-06-25 16:24:51 -07:00
kmap_types.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
kprobes.h [PATCH] x86_64 specific function return probes 2005-06-23 09:45:21 -07:00
ldt.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
linkage.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
local.h [PATCH] x86_64: Correct wrong comment in local.h 2005-04-16 15:25:08 -07:00
mach_apic.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mc146818rtc.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mce.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mman.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mmsegment.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mmu.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mmu_context.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mmx.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mmzone.h [PATCH] reorganize x86-64 NUMA and DISCONTIGMEM config options 2005-06-23 09:45:06 -07:00
module.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mpspec.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
msgbuf.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
msi.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
msr.h [PATCH] x86_64: Fix incorrectly defined MSR_K8_SYSCFG 2005-07-28 21:46:00 -07:00
mtrr.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
namei.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
nmi.h [PATCH] x86_64: Collected NMI watchdog fixes. 2005-05-17 07:59:16 -07:00
node.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
numa.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
numnodes.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
page.h [PATCH] remove hugetlb_clean_stale_pgtable() and fix huge_pte_alloc() 2005-09-05 00:05:46 -07:00
param.h [PATCH] i386: Selectable Frequency of the Timer Interrupt 2005-06-23 09:45:10 -07:00
parport.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
pci-direct.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
pci.h Revert PCIBIOS_MIN_IO changes for 2.6.13 2005-08-14 18:21:30 -07:00
pda.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
percpu.h [PATCH] adjust per_cpu definition in non-SMP case 2005-06-23 09:45:28 -07:00
pgalloc.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
pgtable.h [PATCH] x86_64: avoid some atomic operations during address space destruction 2005-09-05 00:05:48 -07:00
poll.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
posix_types.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
prctl.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
processor.h [PATCH] x86_64: prefetchw() can fall back to prefetch() if !3DNOW 2005-09-07 16:57:15 -07:00
proto.h [PATCH] MTRR suspend/resume cleanup 2005-07-07 18:23:42 -07:00
ptrace.h [PATCH] xen: x86: Rename usermode macro 2005-06-23 09:45:14 -07:00
resource.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
rtc.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
rwlock.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
rwsem.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
scatterlist.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
seccomp.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sections.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
segment.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
semaphore.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sembuf.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
serial.h [PATCH] Serial: Split 8250 port table (part 2) 2005-06-29 18:45:19 +01:00
setup.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
shmbuf.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
shmparam.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sigcontext.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sigcontext32.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
siginfo.h [PATCH] consolidate SIGEV_PAD_SIZE 2005-05-01 08:59:08 -07:00
signal.h [PATCH] asm/signal.h unification 2005-05-04 07:33:15 -07:00
smp.h [PATCH] Fix sync_tsc hang 2005-07-29 15:01:13 -07:00
socket.h [NET]: Introduce SO_{SND,RCV}BUFFORCE socket options 2005-08-29 15:31:35 -07:00
sockios.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sparsemem.h [PATCH] add x86-64 specific support for sparsemem 2005-06-23 09:45:07 -07:00
spinlock.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
stat.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
statfs.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
string.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
suspend.h [PATCH] swsusp: clean assembly parts 2005-06-25 16:24:33 -07:00
swiotlb.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
system.h [PATCH] x86_64: Fix some typos in system.h comments 2005-07-28 21:46:00 -07:00
termbits.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
termios.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
thread_info.h [PATCH] streamline preempt_count type across archs 2005-06-23 09:45:19 -07:00
timex.h [PATCH] Platform SMIs and their interferance with tsc based delay calibration 2005-06-23 09:45:08 -07:00
tlb.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
tlbflush.h [PATCH] x86_64: Fix some comments in tlbflush.h 2005-07-28 21:45:59 -07:00
topology.h [PATCH] sched: sched tuning 2005-06-25 16:24:42 -07:00
types.h [PATCH] sab: consolidate kmem_bufctl_t 2005-09-05 00:05:48 -07:00
uaccess.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
ucontext.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
unaligned.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
unistd.h [PATCH] inotify: add x86-64 syscall entries 2005-07-26 13:37:22 -07:00
user.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
user32.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
vga.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
vsyscall.h [PATCH] x86_64: Add pmtimer support 2005-05-17 07:59:15 -07:00
vsyscall32.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
xor.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00