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10624a97e8
Improvements compared to POWER9 version: 1. Take into account first 16B comparison for aligned strings The previous version compares the first 16B and increments r4 by the number of bytes until the address is 16B-aligned, then starts doing aligned loads at that address. For aligned strings, this causes the first 16B to be compared twice, because the increment is 0. Here we calculate the next 16B-aligned address differently, which avoids that issue. 2. Use simple comparisons for the first ~192 bytes The main loop is good for big strings, but comparing 16B each time is better for smaller strings. So after aligning the address to 16 Bytes, we check more 176B in 16B chunks. There may be some overlaps with the main loop for unaligned strings, but we avoid using the more aggressive strategy too soon, and also allow the loop to start at a 64B-aligned address. This greatly benefits smaller strings and avoids overlapping checks if the string is already aligned at a 64B boundary. 3. Reduce dependencies between load blocks caused by address calculation on loop Doing a precise time tracing on the code showed many loads in the loop were stalled waiting for updates to r4 from previous code blocks. This implementation avoids that as much as possible by using 2 registers (r4 and r5) to hold addresses to be used by different parts of the code. Also, the previous code aligned the address to 16B, then to 64B by doing a few 48B loops (if needed) until the address was aligned. The main loop could not start until that 48B loop had finished and r4 was updated with the current address. Here we calculate the address used by the loop very early, so it can start sooner. The main loop now uses 2 pointers 128B apart to make pointer updates less frequent, and also unrolls 1 iteration to guarantee there is enough time between iterations to update the pointers, reducing stalled cycles. 4. Use new P10 instructions lxvp is used to load 32B with a single instruction, reducing contention in the load queue. vextractbm allows simplifying the tail code for the loop, replacing vbpermq and avoiding having to generate a permute control vector. Reviewed-by: Paul E Murphy <murphyp@linux.ibm.com> Reviewed-by: Raphael M Zinsly <rzinsly@linux.ibm.com> Reviewed-by: Lucas A. M. Magalhaes <lamm@linux.ibm.com> |
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This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 3.2 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: aarch64*-*-linux-gnu alpha*-*-linux-gnu arc*-*-linux-gnu arm-*-linux-gnueabi csky-*-linux-gnuabiv2 hppa-*-linux-gnu i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 ia64-*-linux-gnu m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu riscv32-*-linux-gnu riscv64-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see https://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at https://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see https://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 1996-2015, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.