lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Mon, 20 Apr 2020 21:54:17 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Cc: Alexey Dobriyan <adobriyan@...il.com>, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, pmladek@...e.com, sergey.senozhatsky@...il.com, linux@...musvillemoes.dk Subject: Re: [PATCH 03/15] print_integer: new and improved way of printing integers On Tue, 21 Apr 2020 00:27:23 +0300 Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote: > > > > > TODO > > > benchmark with mainline because nouveau is broken for me -( > > > vsnprintf() changes make the code slower > > > > Exactly main point of this exercise. I don't believe that algos in vsprintf.c > > are too dumb to use division per digit (yes, division by constant which is not > > power of two is a heavy operation). > > > > And second point here, why not to use existing algos from vsprintf.c? Exactly. The code in _print_integer_u32() doesn't look as fast as the code in vsprintf() that happens to use lookup tables and converts without any loops. Hint, loops are bad, they cause the CPU to slow down. Anyway, this patch series would require a pretty good improvement, as the code replacing the sprintf() usages is pretty ugly compared to a simple sprintf() call. Randomly picking patch 6: static int loadavg_proc_show(struct seq_file *m, void *v) { unsigned long avnrun[3]; get_avenrun(avnrun, FIXED_1/200, 0); seq_printf(m, "%lu.%02lu %lu.%02lu %lu.%02lu %u/%d %d\n", LOAD_INT(avnrun[0]), LOAD_FRAC(avnrun[0]), LOAD_INT(avnrun[1]), LOAD_FRAC(avnrun[1]), LOAD_INT(avnrun[2]), LOAD_FRAC(avnrun[2]), nr_running(), nr_threads, idr_get_cursor(&task_active_pid_ns(current)->idr) - 1); return 0; } *vs* static int loadavg_proc_show(struct seq_file *m, void *v) { unsigned long avnrun[3]; char buf[3 * (LEN_UL + 1 + 2 + 1) + 10 + 1 + 10 + 1 + 10 + 1]; char *p = buf + sizeof(buf); int i; *--p = '\n'; p = _print_integer_u32(p, idr_get_cursor(&task_active_pid_ns(current)->idr) - 1); *--p = ' '; p = _print_integer_u32(p, nr_threads); *--p = '/'; p = _print_integer_u32(p, nr_running()); get_avenrun(avnrun, FIXED_1/200, 0); for (i = 2; i >= 0; i--) { *--p = ' '; --p; /* overwritten */ *--p = '0'; /* conditionally overwritten */ (void)_print_integer_u32(p + 2, LOAD_FRAC(avnrun[i])); *--p = '.'; p = _print_integer_ul(p, LOAD_INT(avnrun[i])); } seq_write(m, p, buf + sizeof(buf) - p); return 0; } I much rather keep the first version. -- Steve
Powered by blists - more mailing lists