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Peter Zijlstra 14ea908994 lib/int_sqrt: optimize initial value compute 
commit f8ae107eef209bff29a5816bc1aad40d5cd69a80 upstream.

The initial value (@m) compute is:

	m = 1UL << (BITS_PER_LONG - 2);
	while (m > x)
		m >>= 2;

Which is a linear search for the highest even bit smaller or equal to @x
We can implement this using a binary search using __fls() (or better when
its hardware implemented).

	m = 1UL << (__fls(x) & ~1UL);

Especially for small values of @x; which are the more common arguments
when doing a CDF on idle times; the linear search is near to worst case,
while the binary search of __fls() is a constant 6 (or 5 on 32bit)
branches.

      cycles:                 branches:              branch-misses:

PRE:

hot:   43.633557 +- 0.034373  45.333132 +- 0.002277  0.023529 +- 0.000681
cold: 207.438411 +- 0.125840  45.333132 +- 0.002277  6.976486 +- 0.004219

SOFTWARE FLS:

hot:   29.576176 +- 0.028850  26.666730 +- 0.004511  0.019463 +- 0.000663
cold: 165.947136 +- 0.188406  26.666746 +- 0.004511  6.133897 +- 0.004386

HARDWARE FLS:

hot:   24.720922 +- 0.025161  20.666784 +- 0.004509  0.020836 +- 0.000677
cold: 132.777197 +- 0.127471  20.666776 +- 0.004509  5.080285 +- 0.003874

Averages computed over all values <128k using a LFSR to generate order.
Cold numbers have a LFSR based branch trace buffer 'confuser' ran between
each int_sqrt() invocation.

Link: http://lkml.kernel.org/r/20171020164644.936577234@infradead.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Joe Perches <joe@perches.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Anshul Garg <aksgarg1989@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: David Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Michael Davidson <md@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-04-06 13:43:46 +02:00
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842 A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fonts A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
lz4 A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
lzo A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
mpi A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
raid6 A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
reed_solomon A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
xz A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
zlib_deflate A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
zlib_inflate A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
zstd A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
argv_split.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
asn1_decoder.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
assoc_array.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
atomic64_test.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
atomic64.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
audit.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
bcd.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
bch.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
bitmap.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
bitrev.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
bsearch.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
btree.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
bug.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
build_OID_registry A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
bust_spinlocks.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
check_signature.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
checksum.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
clz_ctz.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
clz_tab.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
cmdline.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
compat_audit.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
cordic.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
cpu_rmap.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
cpu-notifier-error-inject.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
cpumask.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc-ccitt.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc-itu-t.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc-t10dif.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc7.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc8.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc16.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc32.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
crc32defs.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
ctype.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
debug_info.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
debug_locks.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
debugobjects.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
dec_and_lock.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
decompress_bunzip2.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
decompress_inflate.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
decompress_unlz4.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
decompress_unlzma.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
decompress_unlzo.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
decompress_unxz.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
decompress.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
devres.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
digsig.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
div64.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
dma-debug.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
dump_stack.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
dynamic_debug.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
dynamic_queue_limits.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
earlycpio.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
extable.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fault-inject.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fdt_empty_tree.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fdt_ro.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fdt_rw.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fdt_strerror.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fdt_sw.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fdt_wip.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
fdt.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
find_bit.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
flex_array.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
flex_proportions.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
gcd.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
gen_crc32table.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
genalloc.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
glob.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
halfmd4.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
hexdump.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
hweight.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
idr.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
inflate.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
int_sqrt.c lib/int_sqrt: optimize initial value compute 2020-04-06 13:43:46 +02:00
interval_tree_test.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
interval_tree.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
iomap_copy.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
iomap.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
iommu-common.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
iommu-helper.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
ioremap.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
iov_iter.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
irq_regs.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
is_single_threaded.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
jedec_ddr_data.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
kasprintf.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
Kconfig A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
Kconfig.debug A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
Kconfig.kasan A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
Kconfig.kgdb A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
Kconfig.kmemcheck A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
kfifo.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
klist.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
kobject_uevent.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
kobject.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
kstrtox.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
kstrtox.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
lcm.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
libcrc32c.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
list_debug.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
list_sort.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
llist.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-hardirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-mutex.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-rlock-hardirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-rlock-softirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-rlock.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-rsem.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-softirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-spin-hardirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-spin-softirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-spin.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-wlock-hardirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-wlock-softirq.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-wlock.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest-wsem.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
locking-selftest.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
lockref.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
lru_cache.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
Makefile A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
md5.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
memory-notifier-error-inject.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
memweight.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
net_utils.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
nlattr.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
nmi_backtrace.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
notifier-error-inject.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
notifier-error-inject.h A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
of-reconfig-notifier-error-inject.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
oid_registry.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
once.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
parser.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
pci_iomap.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
percpu_counter.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
percpu_ida.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
percpu_test.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
percpu-refcount.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
plist.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
pm-notifier-error-inject.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
proportions.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
radix-tree.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
random32.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
ratelimit.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
rational.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
rbtree_test.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
rbtree.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
reciprocal_div.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
rhashtable.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
scatterlist.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
seq_buf.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
sg_split.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
sha1.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
show_mem.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
smp_processor_id.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
sort.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
stackdepot.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
stmp_device.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
string_helpers.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
string.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
strncpy_from_user.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
strnlen_user.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
swiotlb.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
syscall.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_bpf.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_firmware.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_kasan.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_module.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_printf.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_rhashtable.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_static_key_base.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_static_keys.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test_user_copy.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test-hexdump.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test-kstrtox.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
test-string_helpers.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
textsearch.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
timerqueue.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
ts_bm.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
ts_fsm.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
ts_kmp.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
ucs2_string.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
usercopy.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
uuid.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
vsprintf.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30
xxhash.c A750FXXU4CTBC 2020-03-27 21:51:54 +05:30