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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?d9I15Bha4Gmpdh5DlQQSk/6smS/13ZyR0RFPxp3buMhWYEGGJFSZNWzU9Q7H?= =?us-ascii?Q?8yJA6bjTkZI5h/Sbcdi6DZ8TTYsKUGbF2eXbIeszcJeJVtq97XhEM/b2bqqL?= =?us-ascii?Q?8d0eIg+MIBdAWInT3TftH9SIk2EHSVGOmLzHwb8nxidzmxwyGft29XpFhl76?= =?us-ascii?Q?zbBG0Pq0nwZbGzASRxp3A2x5LjEoMxxR21w47I1HXismt0XK4ukiyjngEMgr?= =?us-ascii?Q?cVN1ZQuIZwft03kOfJDlpE7EUFyd8HfoGiB6KAzawezMYAXLuOgpB8R9JOHD?= =?us-ascii?Q?D5QdU8rHuvJ2232gi/4X1+ZqKHzOi70CAd+p8UXbE20M1pMqlEJB2Th62t4P?= =?us-ascii?Q?u+YLmvxVK5ti3I2NL9FszJBgW9kFOP2Y02s3qJqnCHRw8ncXh9gLP6L2bZbw?= =?us-ascii?Q?6VAQP9P7suZf8Z7dF4WjxA65tB2ujT4zm8Be/d6VNMVSl/IrACFtAnSAw2Xp?= =?us-ascii?Q?vQXaJxE5mb5AOwPu01946DNuify7IdZszno0HIAQGRkO5Wi7y4ib0QzzFZL8?= =?us-ascii?Q?VawL8MzN7murW9CuP5PA/FdrCSZnrhZ2M4qaYPdb+FNlbjfOWbq6ofBHBUfq?= =?us-ascii?Q?rDUtdR+TCVvDOzORWDzpevBDW8v0U8eDsdz0NdHYj1i6btUxHVQp/rFC+8uT?= =?us-ascii?Q?htcsvpwSNgxG2lVMYGxKPt53O0ouDEASsSik5QSbS7LP9XhKAClS8M/Ic9Bb?= =?us-ascii?Q?KV2cY5JfDD/V2yyZhVs1arhXM1sNHEsXx8e2g+QZlRiaT6ZfDtP/a/Pf2C7z?= =?us-ascii?Q?nvpI+937nvcjERAHzOfyNFOTo9zT1MZcJyvXeOrWYqrUYuV+Np0d8r2954+V?= =?us-ascii?Q?zFTofpaspvxhO8a/IhA94cXCSRrPgcLIpBgrmftQ4RXaK6vD0lWj/37PjoKU?= =?us-ascii?Q?y4xE33uK3hIDBHr5R0QKESDktNtDvqqkbi2EV2PUsCecu/dayhv+SLCH6mBs?= =?us-ascii?Q?yyvOK/TKbLeJdEJNBREwOrh8cMB9TG6YvK2xwml8mqLhVn39u9x4R9jLH0bu?= =?us-ascii?Q?yTGnu+kQ4hmz/zHwn/OFRVqfHx+P+Fdlphoppbu629fqUiwgMWPXyUrsEWLh?= =?us-ascii?Q?9mMtyykJNVzu8SG3JlKMI2egmxHe8MLecUTARdaAhk1qsRRNKVNy9fuZHZjm?= =?us-ascii?Q?6PU3OrEjzgMTv8cPEEA5WgcQELZAxEZpWL1hqJa9Bx8vPLJMWplzaiLcifnM?= =?us-ascii?Q?WqOPxPlYeuz2LQ+TvRC5yxsm+V1Y7ZHHes7me2vopPKKEdb+T5bma0R7hynb?= =?us-ascii?Q?sbUWlJ7Tglz15pbjGoK3dI0UN2njZuz87IoZPLPdgTkJdzUXhGjJK6bLnffj?= =?us-ascii?Q?qLnYpT0TQWxWbPfPpI5VixqUug2mtYE+ZpucyH+0jk9gtBfcSVSnoN05Zjui?= =?us-ascii?Q?vo/+vrYmAPlFP7qB92Ggt/vfeskp8F/V81XTm9EMvNbg+fE4P5ObqQrRjX47?= =?us-ascii?Q?Nika9Tj2A/zLVZmRfaagMAjR0nG7M9QXS+9u1CvQNM3QwTqVnt9UyAwN2kIt?= =?us-ascii?Q?HjpNMcqT2oe45ztZgUZcNp/gFze1sY+rGsagLzHXPGnO6CPki30ybM4Poq2v?= =?us-ascii?Q?kALzIV6oEPdmL0qLElEKg66ioDLXTVPghE+nE4/FLi6vTEasVxcJTqU/pOl7?= =?us-ascii?Q?Z7gHEYhjgej4LsQaiPQNLz1veSDWViB3qtqpcnIBfoOZSXybdy4OE24ecHv3?= =?us-ascii?Q?j/BM3I5SWdmd3rQxqge/bVnapBJ9x+C5NIfG7Pv/b/FPFZeC3xjPY8kC+fJL?= =?us-ascii?Q?5kJOmdYRBQ=3D=3D?= X-OriginatorOrg: atomlin.com X-MS-Exchange-CrossTenant-Network-Message-Id: 22ed4307-dc48-47bb-1866-08df24017650 X-MS-Exchange-CrossTenant-AuthSource: CWLP123MB6607.GBRP123.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Oct 2026 23:28:00.9714 (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: RfKz36eHpW+qBTjlmwjLnmTD7AWdIGfeiJ6D5Wb+WEtW2kp6wE8Rs9t2zSnH63+oXvFlhiAvFS6p7eB9uF2ikg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CWLP123MB4004 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 | 52 ++++++++++++++++++++++++++++++------- 1 file changed, 43 insertions(+), 9 deletions(-) diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c index 6017493ff179..4e77a0b2513f 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, }; @@ -767,6 +771,13 @@ 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"); @@ -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); @@ -832,14 +851,29 @@ 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: + free(buf); + strbuf_release(&linebuf); close(trace_fd); out_reset: exit_tracing_instance(); -- 2.55.0