Hi Steven, Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on tip/perf/core] [also build test WARNING on linux/master linus/master v5.8-rc2 next-20200625] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Steven-Rostedt/ring-buffer-Have-nested-events-still-record-running-time-stamp/20200626-105715 base: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git bb42b3d39781d7fcd3be7f9f9bf11b6661b5fdf1 config: mips-allyesconfig (attached as .config) compiler: mips-linux-gcc (GCC) 9.3.0 reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=mips If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <l...@intel.com> All warnings (new ones prefixed by >>): kernel/trace/ring_buffer.c: In function '__rb_reserve_next': kernel/trace/ring_buffer.c:2911:6: warning: unused variable 'delta' [-Wunused-variable] 2911 | u64 delta, before, after; | ^~~~~ >> kernel/trace/ring_buffer.c:2910:32: warning: variable 'next' set but not >> used [-Wunused-but-set-variable] 2910 | unsigned long tail, write, w, next; | ^~~~ vim +/next +2910 kernel/trace/ring_buffer.c 2903 2904 static struct ring_buffer_event * 2905 __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer, 2906 struct rb_event_info *info) 2907 { 2908 struct ring_buffer_event *event; 2909 struct buffer_page *tail_page; > 2910 unsigned long tail, write, w, next; 2911 u64 delta, before, after; 2912 bool abs = false; 2913 2914 /* Don't let the compiler play games with cpu_buffer->tail_page */ 2915 tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page); 2916 2917 /*A*/ w = local_read(&tail_page->write) & RB_WRITE_MASK; 2918 barrier(); 2919 before = local64_read(&cpu_buffer->before_stamp); 2920 after = local64_read(&cpu_buffer->write_stamp); 2921 barrier(); 2922 info->ts = rb_time_stamp(cpu_buffer->buffer); 2923 2924 if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) { 2925 info->delta = info->ts; 2926 abs = true; 2927 } else { 2928 info->delta = info->ts - after; 2929 } 2930 2931 if (unlikely(test_time_stamp(info->delta))) 2932 rb_handle_timestamp(cpu_buffer, info); 2933 2934 /* 2935 * If interrupting an event time update, we may need an absolute timestamp. 2936 * Don't bother if this is the start of a new page (w == 0). 2937 */ 2938 if (unlikely(before != after && w)) 2939 info->add_timestamp = RB_ADD_STAMP_FORCE; 2940 /* 2941 * If the time delta since the last event is too big to 2942 * hold in the time field of the event, then we append a 2943 * TIME EXTEND event ahead of the data event. 2944 */ 2945 if (unlikely(info->add_timestamp)) 2946 info->length += RB_LEN_TIME_EXTEND; 2947 2948 next = READ_ONCE(cpu_buffer->next_write); 2949 WRITE_ONCE(cpu_buffer->next_write, w + info->length); 2950 2951 /*B*/ local64_set(&cpu_buffer->before_stamp, info->ts); 2952 2953 /*C*/ write = local_add_return(info->length, &tail_page->write); 2954 2955 /* set write to only the index of the write */ 2956 write &= RB_WRITE_MASK; 2957 2958 tail = write - info->length; 2959 2960 /* See if we shot pass the end of this buffer page */ 2961 if (unlikely(write > BUF_PAGE_SIZE)) { 2962 if (tail != w) { 2963 /* before and after may now different, fix it up*/ 2964 before = local64_read(&cpu_buffer->before_stamp); 2965 after = local64_read(&cpu_buffer->write_stamp); 2966 if (before != after) 2967 (void)local64_cmpxchg(&cpu_buffer->before_stamp, before, after); 2968 } 2969 return rb_move_tail(cpu_buffer, tail, info); 2970 } 2971 2972 if (likely(tail == w)) { 2973 u64 save_before; 2974 2975 /* Nothing interrupted us between A and C */ 2976 /*D*/ local64_set(&cpu_buffer->write_stamp, info->ts); 2977 barrier(); 2978 /*E*/ save_before = local64_read(&cpu_buffer->before_stamp); 2979 if (likely(info->add_timestamp != RB_ADD_STAMP_FORCE)) 2980 /* This did not interrupt any time update */ 2981 info->delta = info->ts - after; 2982 else 2983 /* Just use full timestamp for inerrupting event */ 2984 info->delta = info->ts; 2985 barrier(); 2986 if (unlikely(info->ts != save_before)) { 2987 /* SLOW PATH - Interrupted between C and E */ 2988 2989 after = local64_read(&cpu_buffer->write_stamp); 2990 /* Write stamp must only go forward */ 2991 if (save_before > after) { 2992 /* 2993 * We do not care about the result, only that 2994 * it gets updated atomically. 2995 */ 2996 (void)local64_cmpxchg(&cpu_buffer->write_stamp, after, save_before); 2997 } 2998 } 2999 } else { 3000 u64 ts; 3001 /* SLOW PATH - Interrupted between A and C */ 3002 after = local64_read(&cpu_buffer->write_stamp); 3003 ts = rb_time_stamp(cpu_buffer->buffer); 3004 barrier(); 3005 /*E*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) && 3006 after < ts) { 3007 /* Nothing came after this event between C and E */ 3008 info->delta = ts - after; 3009 (void)local64_cmpxchg(&cpu_buffer->write_stamp, after, info->ts); 3010 info->ts = ts; 3011 } else { 3012 /* 3013 * Interrupted beween C and E: 3014 * Lost the previous events time stamp. Just set the 3015 * delta to zero, and this will be the same time as 3016 * the event this event interrupted. And the events that 3017 * came after this will still be correct (as they would 3018 * have built their delta on the previous event. 3019 */ 3020 info->delta = 0; 3021 } 3022 if (info->add_timestamp == RB_ADD_STAMP_FORCE) 3023 info->add_timestamp = RB_ADD_STAMP_NORMAL; 3024 } 3025 3026 /* 3027 * If this is the first commit on the page, then it has the same 3028 * timestamp as the page itself. 3029 */ 3030 if (unlikely(!tail && info->add_timestamp != RB_ADD_STAMP_FORCE && !abs)) 3031 info->delta = 0; 3032 3033 /* We reserved something on the buffer */ 3034 3035 event = __rb_page_index(tail_page, tail); 3036 rb_update_event(cpu_buffer, event, info); 3037 3038 local_inc(&tail_page->entries); 3039 3040 /* 3041 * If this is the first commit on the page, then update 3042 * its timestamp. 3043 */ 3044 if (!tail) 3045 tail_page->page->time_stamp = info->ts; 3046 3047 /* account for these added bytes */ 3048 local_add(info->length, &cpu_buffer->entries_bytes); 3049 3050 return event; 3051 } 3052 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-...@lists.01.org
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