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Peter Anvin" , x86@kernel.org, Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Mathieu Desnoyers , David Hildenbrand , Jonathan Corbet , Matthew Wilcox , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-doc@vger.kernel.org References: <20260714182243.10687-1-wangjinchao600@gmail.com> <20260714183206.12688-1-wangjinchao600@gmail.com> <20260714171438.226faf7b@gandalf.local.home> Content-Language: en-US From: Jinchao Wang In-Reply-To: <20260714171438.226faf7b@gandalf.local.home> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/14/2026 5:14 PM, Steven Rostedt wrote: > On Wed, 15 Jul 2026 02:32:06 +0800 > Jinchao Wang wrote: > >> --- /dev/null >> +++ b/include/trace/events/kwatch.h >> @@ -0,0 +1,57 @@ >> +/* SPDX-License-Identifier: GPL-2.0 */ >> +#undef TRACE_SYSTEM >> +#define TRACE_SYSTEM kwatch >> + >> +#if !defined(_TRACE_KWATCH_H) || defined(TRACE_HEADER_MULTI_READ) >> +#define _TRACE_KWATCH_H >> + >> +#include >> +#include >> + >> +#define KWATCH_STACK_DEPTH 8 >> + >> +struct trace_seq; >> +const char *kwatch_trace_print_stack(struct trace_seq *p, >> + const unsigned long *stack, >> + unsigned int nr); >> + >> +TRACE_EVENT(kwatch_hit, >> + TP_PROTO(unsigned long ip, unsigned long sp, unsigned long addr, >> + u64 time_ns, >> + unsigned long *stack_entries, unsigned int stack_nr), >> + TP_ARGS(ip, sp, addr, time_ns, stack_entries, stack_nr), >> + >> + TP_STRUCT__entry( >> + __field(unsigned long, ip) >> + __field(unsigned long, sp) >> + __field(unsigned long, addr) >> + __field(u64, time_ns) > > Move the time_ns to the first field, as unsigned long on 32 bit > architectures is 4 bytes, and this will make 4 byte "hole" in the event. Will fix in v2.> > >> + __field(unsigned int, stack_nr) > > Make stack_nr the last element for the same reason. Will fix in v2. > >> + __array(unsigned long, stack, KWATCH_STACK_DEPTH) > > Make the above a dynamic array based on stack entries. > > __dynamic_array(unsigned long, stack, min_t(unsigned int, stack_nr, > KWATCH_STACK_DEPTH); Much better than always paying for the full depth - will convert to __dynamic_array (and use __get_dynamic_array() in TP_fast_assign and TP_printk as you showed) in v2. Thank you for the review! Thanks, Jinchao > > >> + ), >> + >> + TP_fast_assign( >> + unsigned int i; > unsigned long *stack = __get_dynamic_array(stack); >> + >> + __entry->ip = ip; >> + __entry->sp = sp; >> + __entry->addr = addr; >> + __entry->time_ns = time_ns; >> + __entry->stack_nr = min_t(unsigned int, stack_nr, >> + KWATCH_STACK_DEPTH); >> + for (i = 0; i < __entry->stack_nr; i++) >> + __entry->stack[i] = stack_entries[i]; > > stack[i] = stack_entries[i]; > >> + ), >> + >> + TP_printk("KWatch HIT: time=%llu.%06lu ip=%pS addr=0x%lx%s", >> + __entry->time_ns / 1000000000ULL, >> + (unsigned long)((__entry->time_ns / 1000ULL) % 1000000ULL), >> + (void *)__entry->ip, __entry->addr, >> + kwatch_trace_print_stack(p, __entry->stack, > > kwatch_trace_print_stack(p, __get_dynamic_array(stack), > >> + __entry->stack_nr)) >> +); >> + > > -- Steve