| Message ID | 20210129204528.2118168-1-yury.norov@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | lib/find_bit: fast path for small bitmaps | expand |
On Fri, Jan 29, 2021 at 12:45 PM Yury Norov <yury.norov@gmail.com> wrote: > > Bitmap operations are much simpler and faster in case of small bitmaps, whicn > fit into a single word. In linux/bitmap.h we have a machinery that allows > compiler to replace actual function call with a few instructions if bitmaps > passed into the function is small and its size is known at compile time. > > find_*_bit() API lacks this functionality; despite users will benefit from it > a lot. One important example is cpumask subsystem, when NR_CPUS <= BITS_PER_LONG. > In the very best case, the compiler may replace a find_*_bit() call for such a > bitmap with a single ffs or ffz instruction. > > Tools is synchronized with new implementation where needed. Sorry for the broken enumeration . If it's too confusing, please let me know and I'll resend.
On Fri, Jan 29, 2021 at 10:54 PM Yury Norov <yury.norov@gmail.com> wrote: > On Fri, Jan 29, 2021 at 12:45 PM Yury Norov <yury.norov@gmail.com> wrote: > > > > Bitmap operations are much simpler and faster in case of small bitmaps, whicn > > fit into a single word. In linux/bitmap.h we have a machinery that allows > > compiler to replace actual function call with a few instructions if bitmaps > > passed into the function is small and its size is known at compile time. > > > > find_*_bit() API lacks this functionality; despite users will benefit from it > > a lot. One important example is cpumask subsystem, when NR_CPUS <= BITS_PER_LONG. > > In the very best case, the compiler may replace a find_*_bit() call for such a > > bitmap with a single ffs or ffz instruction. > > > > Tools is synchronized with new implementation where needed. > > Sorry for the broken enumeration . If it's too confusing, please let me know > and I'll resend. Yeah, please resend with a bumped version and respective changelog.
Bitmap operations are much simpler and faster in case of small bitmaps, whicn fit into a single word. In linux/bitmap.h we have a machinery that allows compiler to replace actual function call with a few instructions if bitmaps passed into the function is small and its size is known at compile time. find_*_bit() API lacks this functionality; despite users will benefit from it a lot. One important example is cpumask subsystem, when NR_CPUS <= BITS_PER_LONG. In the very best case, the compiler may replace a find_*_bit() call for such a bitmap with a single ffs or ffz instruction. Tools is synchronized with new implementation where needed. Yury Norov (6): arch: rearrange headers inclusion order in asm/bitops for m68k and sh lib: inttroduce BITS_{FIRST,LAST}() macro bits_per_long.h: introduce SMALL_CONST() macro lib: inline _find_next_bit() wrappers lib: add fast path for find_next_*_bit() lib: add fast path for find_first_*_bit() and find_last_bit() arch/m68k/include/asm/bitops.h | 4 +- arch/sh/include/asm/bitops.h | 3 +- include/asm-generic/bitops/find.h | 108 +++++++++++++++++++++--- include/asm-generic/bitops/le.h | 38 ++++++++- include/asm-generic/bitsperlong.h | 2 + include/linux/bitmap.h | 60 ++++++------- include/linux/bitops.h | 12 --- include/linux/bits.h | 6 ++ include/linux/cpumask.h | 8 +- include/linux/netdev_features.h | 2 +- include/linux/nodemask.h | 2 +- lib/bitmap.c | 26 +++--- lib/find_bit.c | 72 +++------------- lib/genalloc.c | 8 +- tools/include/asm-generic/bitops/find.h | 85 +++++++++++++++++-- tools/include/asm-generic/bitsperlong.h | 2 + tools/include/linux/bitmap.h | 39 +++------ tools/include/linux/bits.h | 6 ++ tools/lib/bitmap.c | 6 +- tools/lib/find_bit.c | 56 +++++------- tools/testing/radix-tree/bitmap.c | 4 +- 21 files changed, 330 insertions(+), 219 deletions(-)