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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?0KHdGBX7Ntzkfn22ilQG+SWmIQLGMNfVPauWXA4GG9GRQbJ2d0L2BM6YqybE?= =?us-ascii?Q?HX8RUzCGs59UHfS4WI9Rl3CVMyo20Thm3kLTJoxU/o00E7RXYVkVCnebP/V1?= =?us-ascii?Q?PTrsLN9bBapjrujxx2tKRSaj0U8vBWPunvYyJ1xlcX8RzQMFXchPtvyorDbv?= =?us-ascii?Q?NjLA+nfqp7CtZ0WLVVxX4Akzif0hP1zWmV2beZwTI1Y9j+gb7IeybsbmVNNK?= =?us-ascii?Q?WfIwneolBUrASg63G9zktXkeCfYaLuzt+6yxqJvmET8lZLFGemNyGOkHlb6q?= =?us-ascii?Q?hw5XLtpKiGw9IIQQKtod3M9d/nUOh1TtS0ckVEwUQAiML+It1eqken+yziGQ?= =?us-ascii?Q?NQ7LcT3K3Pl1fESFu2zivA14/HfGzGC5Txb1mJYeqWVpPF1wea00CLbTJmhd?= =?us-ascii?Q?A4H7gFWHgrGo6MYX1kWTwa7PI1AcE14GtvQmGFynP02YNNXvB0B621FGP6bb?= =?us-ascii?Q?/rFnkHI0FG703VF0oRxkTkKtl5wTiD/JyETwp8PUirhjbySHaTdKYVsnYTJa?= =?us-ascii?Q?m3m2JFN6GInf/dD3gh79iUyN2fjo6lETeV+oWSngE9yjp9H6H3taNhogEvLw?= =?us-ascii?Q?fAT1cG+k1JODA24OHBmI6OBAPCfdBaS8J7yDRWNn/AoR/Q/EXIHwm13rS2oY?= =?us-ascii?Q?TDoF6yoCfguy5pczVZc0aby/tzEga5ePJJDGr0buudC2XIEQQZdbHnzY15nv?= =?us-ascii?Q?cTGPaos5mGV8lFGtRz6DGZAbKcTneyYqw+BSsUaB1zhqkxfS/vMiWqrbObuy?= =?us-ascii?Q?WtkgznSdLBRJw7L4L0P5AKMZqkHMoZ+wK12lo0i1yZCEFsxUegL9XNQa/1+a?= =?us-ascii?Q?SUWNIQF+r9F2uSMcu7xNePmW8UqzkRxrD83z1+rwRMPyKWHPAadva6hfb7Ob?= =?us-ascii?Q?CvXC702EUKnJyWOpc/ENQX5pjJ2YwsF4P9vNomtZNI2RMcQ0DWteB7h3by0/?= =?us-ascii?Q?ljymldV8CMcb5rOOMUJQsMecS13mvNai0B4q+8jDAuQBDajXt4RoTPFasq8G?= =?us-ascii?Q?dlHoNVeNiEfnNEHps7FTk9AUe2mkA8WBu9XPpkWVVhrHzU8WlRTwRFJxNO/k?= =?us-ascii?Q?qL4bvUcF6gktqnlHcuvbcaYqp5fYVAexkScMkWv03+T2Hxu4FTDIymAHVmeA?= =?us-ascii?Q?O0myYn/YyisoUEx4zvq6wxtFGbnrLIedr4NWAmRNsYnvmWLKY+a9JGpjp0OV?= =?us-ascii?Q?mWRgKB5hNYr1Rg5X8NzNM3eu6iAIn7nqHUpzBLh0jut3kz5lKduU1j6nk8Jg?= =?us-ascii?Q?5/iAuOCdyVkrtwyCi82TH0gCSfK9pWr/pBfqtp+WtYjItr4r0KAWxJBoZb3m?= =?us-ascii?Q?5+KCdlyuqnGOnszlJy7rL2YJbATuSY3qJAVfrwYB0FTUGu61vPMJ7xLNz2Zo?= =?us-ascii?Q?dDY/fpiuhHQlQKgAX3RBTnO6ZmGxBuFBbvm7AGXl4H/icnRwrqYMiYGNVD03?= =?us-ascii?Q?1qxzkHzQbVRQqBfjmNwiL+7/kHcCC9O/HEDvBR9a98QQv6GJLZzKFnbWhnXp?= =?us-ascii?Q?5vMPjqW+Oj+BiLqClBucviCqp6kQAwh7n2p67Lsg7v6D4Z63TiRnVdYIJXUQ?= =?us-ascii?Q?iRZxVzBcUzIofYUoG5MZDQDUreMBWXS77fwqQdYhzmugnRWCQ4CePsnpFaCK?= =?us-ascii?Q?jjpGTYqWbQvhrzwhZto+vXsMMDwf1Kh3fnmLvaT+nKnn9qnTOh/p/ilcSmm3?= =?us-ascii?Q?CMm8rD3IFoghrYligEvMMcBypWjcuw38GnP0IxHN+earq5tzUWtB6mLQTuYB?= =?us-ascii?Q?7SB+X+UBEA=3D=3D?= X-OriginatorOrg: atomlin.com X-MS-Exchange-CrossTenant-Network-Message-Id: 968262b6-9c09-41b2-4e91-08df27f8011d X-MS-Exchange-CrossTenant-AuthSource: CWLP123MB6607.GBRP123.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Oct 2026 00:30:23.5618 (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: ES0wAOUx2cdbULW24MFrlBT82h4x/bGHwdmduQyN/hYVf0ALTZ2elkzbGmvdaN5NmtaG1fMUAw61WzGyg7dSEA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: LOVP123MB8542 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, while the stack frame of __cmd_ftrace() is reduced by over 96% (down to ~160 bytes). Signed-off-by: Aaron Tomlin --- tools/perf/builtin-ftrace.c | 57 ++++++++++++++++++++++++++++++------- 1 file changed, 46 insertions(+), 11 deletions(-) diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c index 6017493ff179..d6604be593a3 100644 --- a/tools/perf/builtin-ftrace.c +++ b/tools/perf/builtin-ftrace.c @@ -41,7 +41,10 @@ #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; @@ -738,7 +741,8 @@ 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, }; @@ -767,10 +771,17 @@ 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); + 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); @@ -779,7 +790,7 @@ 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); @@ -810,11 +821,19 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) break; if (pollfd.revents & POLLIN) { - int n = read(trace_fd, buf, sizeof(buf)); - if (n < 0) - break; - if (fwrite(buf, n, 1, stdout) != 1) + int n = read(trace_fd, buf, TRACE_BUF_SIZE); + + if (n <= 0) break; + for (int i = 0; i < n; i++) { + if (buf[i] == '\n') { + fprintf(stdout, "%s\n", linebuf.buf); + 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 */ fflush(stdout); } @@ -823,7 +842,7 @@ 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); @@ -832,15 +851,31 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace) /* read remaining buffer contents */ while (true) { - int n = read(trace_fd, buf, sizeof(buf)); + int n = read(trace_fd, buf, TRACE_BUF_SIZE); + if (n <= 0) break; - if (fwrite(buf, n, 1, stdout) != 1) - break; + for (int i = 0; i < n; i++) { + if (buf[i] == '\n') { + fprintf(stdout, "%s\n", linebuf.buf); + strbuf_setlen(&linebuf, 0); + } else { + if (strbuf_addch(&linebuf, buf[i]) < 0) + goto out_close_fd; + } + } + } + + if (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