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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?cNQzCrdNgy0coWUckFxvpX7FDU4uKQ50jvQyHxvVAQVzVEQwz8nkG3DHmGj9?= =?us-ascii?Q?BzVATzVNqG/qvJcVXXlKhB3QKrdu9f4vtsvAzDYFu0kFku2kWOYnZt75uxVf?= =?us-ascii?Q?oodBxJZFC/YIghMrofYcnPUkKCoElTtNIvH36A2smqZgC6aGgJiTjAgckx7m?= =?us-ascii?Q?ghdFhuQYjvpRhqunr3PY78sBraJvhypAlizRXVHsTjovizzQQC7IvImyIkdt?= =?us-ascii?Q?/jKPi0pPABtDJRysXAuqRP980tVMYIrnVYq6lwiwHbzLWcBbZiIumDBOE4fm?= =?us-ascii?Q?Wq7vU//l01AdM3fXviCOQEc8Cdh6UBtw9cKOWlX8QxXLe1XwU2OVvn591JG1?= =?us-ascii?Q?neiUJ+tGU7d2ATNmY8z7XBTff66Ue67dxl2/4RSmoZ90STuJ07CpARw8RczQ?= =?us-ascii?Q?wlWLL+GJar2ASoLhYA5Nqg1uj2PTjU63j1uOzIRXFLiB96kJNXrPle9J6IOt?= =?us-ascii?Q?Rcaleaac5b6I2/KI01pB90kkaYBMMGeLAWqKuxSi2thWIsS9L0kqeVayBkFL?= =?us-ascii?Q?+zyhTf9BqcNFhrB+xFVajq0W7ANxw57alW2Bj++reOpgFh8ynkFtcYR65FDL?= =?us-ascii?Q?1FBGTi4Kjj4l3yblMw/xHe+VGB5x7zMXJSZEWjeljilNiBdl5O0XLmqoyA4b?= =?us-ascii?Q?pkZAP5hYg0Db6vHw9JFYTMbPPSzn/qSGY1dUpOjKEx673KzaCMSRw4mwFanh?= =?us-ascii?Q?MV1FGEqGWe+EXELrX817vBqljkEN3zof1G/4bGQuZC+sJDTYfZuiLGZaw/TM?= =?us-ascii?Q?HyZYt1/YwuaQhO91QYwjx7CCJpeNpkTxJDdAYv+ttXO3mssfCVnb/+/59Vaz?= =?us-ascii?Q?EzyOSiq+BFmsnU/W6cXkA6njFfqAgjtAsDB0Upfxeju6q6ApWOpcsLt/PTLL?= =?us-ascii?Q?reMxgKb+D7Q7/hXoujjkyKuqCtxsw2XzVEzT28aHpT0Vw0LPyBzUsHO5+Rf2?= =?us-ascii?Q?uOVuhbjIliWmKm6sN8AbID9ywpqzV5HeRaEZnugeg4gBHgTwJpTwWunQ7Y0F?= =?us-ascii?Q?ALJZlgMTC+HhgD2dsuJCTAc2HVr78HDyYOIKXkEFoMLoNdJDVmz9+4BMQNJx?= =?us-ascii?Q?Hpm0R4wuao/Bku/RkVMP3XasZZYhG54n2Lm+ThkWPlkQ8MFLOinuaFvyuXZL?= =?us-ascii?Q?c9eHbDAzSJamgtsCRieP/ssz1sp+PeI4sjrYuBpjoEHF9PbadRoIqxB6iKT1?= =?us-ascii?Q?xDRQE0Vs5/Gps/oSGQ11M+vUQ6+9nNehb7GZcEztt0GwTk5Pgd9ItVzrglsK?= =?us-ascii?Q?vof8EnG/7TefxSYbtLzqd1nQ0msfvQ8x+gBPZWBnYTdHTGugCnrbHpzJeX42?= =?us-ascii?Q?VTUeLr0Ql6WMHrGxEhCkN0o6FiJZIeRPWTc/89laehdl8rjbT7jiO3f6Xv+X?= =?us-ascii?Q?vzKtF1WpfrBUCkuPYxJckFn1LtSf8Lpy9rj5X2xxUvX52dL7GErQ1QVmVVy3?= =?us-ascii?Q?IMog5do9dA5kLjYvlJFaQs9oWCkFx/r224hXRO9kmiHND4liMmiq/Z6lPGrc?= =?us-ascii?Q?3UXrcVV66COmkmd9ES0EA1m2Xn3gpAMhppH/wxVSnMFMNWeffXb5ZyfTd2DO?= =?us-ascii?Q?z20y9j8CFNhBqh7YutYnVJd8VmJ0EGgu04iOqZaOH0KzfRldfK5oMnIBkpe8?= =?us-ascii?Q?1o6HDHJnNvqGm0B2JlQJSaI1tzSQQ7qpOmFaEd3JLR92hHBuBjJjLNIzitob?= =?us-ascii?Q?+zdLCds2oS81O5bsIqP32cM7TSpDgbuAnhzg83vJg0i00PVKNmr49wdZfMe5?= =?us-ascii?Q?dfGFpUegaQ=3D=3D?= X-OriginatorOrg: atomlin.com X-MS-Exchange-CrossTenant-Network-Message-Id: 4d84597b-82a8-46f3-1608-08df321566df X-MS-Exchange-CrossTenant-AuthSource: CWLP123MB6607.GBRP123.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Oct 2026 21:26:01.2959 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: e6a32402-7d7b-4830-9a2b-76945bbbcb57 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: oojggfN814RWmww3xDgwRcJyX+uZhFcuEXO3CLN2VsM5AcsyUJQdP5TxB3mlcxEtmLzfUMnDhg53+RQ5jLP+Zw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: LO4P123MB6642 In __cmd_ftrace(), incoming trace data from trace_pipe was historically buffered in a fixed 4096-byte array allocated directly on the stack frame. Furthermore, reads were written directly to stdout via fwrite() in arbitrary chunk sizes, rather than as discrete, well-delimited trace lines. Refactor __cmd_ftrace() to employ dynamic heap allocation for the read buffer alongside a dynamic struct strbuf to accumulate streamed characters into whole lines. Pre-allocating the strbuf ensures that line processing incurs zero heap reallocations during steady-state polling, whilst the stack frame of __cmd_ftrace() is reduced by over 96% (down to ~160 bytes). Emitting complete lines provides discrete records necessary for subsequent call graph parsing and inlined function reconstruction. Signed-off-by: Aaron Tomlin --- tools/perf/builtin-ftrace.c | 56 ++++++++++++++++++++++++++++++------- 1 file changed, 46 insertions(+), 10 deletions(-) diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c index 7cdc9ae2fbbb..65983259b07e 100644 --- a/tools/perf/builtin-ftrace.c +++ b/tools/perf/builtin-ftrace.c @@ -42,7 +42,10 @@ #include "util/units.h" #include "util/parse-sublevel-options.h" +#include "util/strbuf.h" + #define DEFAULT_TRACER "function_graph" +#define TRACE_BUF_SIZE 4096 static volatile sig_atomic_t workload_exec_errno; static volatile sig_atomic_t done; @@ -739,7 +742,8 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) { char *trace_file; int trace_fd; - char buf[4096]; + char *buf = NULL; + struct strbuf linebuf = STRBUF_INIT; struct pollfd pollfd = { .events = POLLIN, }; @@ -768,10 +772,18 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) setup_pager(); + buf = malloc(TRACE_BUF_SIZE); + if (!buf) { + pr_err("failed to allocate trace buffer\n"); + goto out_reset; + } + strbuf_init(&linebuf, 512); + strbuf_setlen(&linebuf, 0); + trace_file = get_tracing_instance_file("trace_pipe"); if (!trace_file) { pr_err("failed to open trace_pipe\n"); - goto out_reset; + goto out_free; } trace_fd = open(trace_file, O_RDONLY); @@ -780,7 +792,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) if (trace_fd < 0) { pr_err("failed to open trace_pipe\n"); - goto out_reset; + goto out_free; } fcntl(trace_fd, F_SETFL, O_NONBLOCK); @@ -814,7 +826,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) } if (pollfd.revents & POLLIN) { - int n = read(trace_fd, buf, sizeof(buf)); + int n = read(trace_fd, buf, TRACE_BUF_SIZE); if (n < 0) { if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR) @@ -823,8 +835,16 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) } if (n == 0) break; - if (fwrite(buf, n, 1, stdout) != 1) - break; + for (int i = 0; i < n; i++) { + if (buf[i] == '\n') { + if (fprintf(stdout, "%s\n", linebuf.buf) < 0) + break; + strbuf_setlen(&linebuf, 0); + } else { + if (strbuf_addch(&linebuf, buf[i]) < 0) + goto out_close_fd; + } + } /* flush output since stdout is in full buffering mode due to pager */ if (fflush(stdout) < 0 || ferror(stdout)) break; @@ -834,7 +854,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) write_tracing_file("tracing_on", "0"); if (workload_exec_errno) { - const char *emsg = str_error_r(workload_exec_errno, buf, sizeof(buf)); + const char *emsg = str_error_r(workload_exec_errno, buf, TRACE_BUF_SIZE); /* flush stdout first so below error msg appears at the end. */ fflush(stdout); pr_err("workload failed: %s\n", emsg); @@ -843,7 +863,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) /* read remaining buffer contents */ while (!ferror(stdout)) { - int n = read(trace_fd, buf, sizeof(buf)); + int n = read(trace_fd, buf, TRACE_BUF_SIZE); if (n < 0) { if (errno == EINTR) @@ -852,12 +872,28 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) } if (n == 0) break; - if (fwrite(buf, n, 1, stdout) != 1) - break; + for (int i = 0; i < n; i++) { + if (buf[i] == '\n') { + if (fprintf(stdout, "%s\n", linebuf.buf) < 0) + break; + strbuf_setlen(&linebuf, 0); + } else { + if (strbuf_addch(&linebuf, buf[i]) < 0) + goto out_close_fd; + } + } + } + + if (!ferror(stdout) && linebuf.len > 0) { + fprintf(stdout, "%s\n", linebuf.buf); + strbuf_setlen(&linebuf, 0); } out_close_fd: close(trace_fd); +out_free: + free(buf); + strbuf_release(&linebuf); out_reset: exit_tracing_instance(); out: -- 2.55.0