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The struct dump_regs contains 512 bytes of cache_regs, meaning the two values in perf_sample contribute 1088 bytes of its total 1384 bytes size. Initializing this much memory has a cost reported by Tavian Barnes <tavianator@tavianator.com> as about 2.5% when running `perf script --itrace=i0`: https://lore.kernel.org/lkml/d841b97b3ad2ca8bcab07e4293375fb7c32dfce7.1736618095.git.tavianator@tavianator.com/ Adrian Hunter <adrian.hunter@intel.com> replied that the zero initialization was necessary and couldn't simply be removed. This patch aims to strike a middle ground of still zeroing the perf_sample, but removing 79% of its size by make user_regs and intr_regs optional pointers to zalloc-ed memory. To support the allocation accessors are created for user_regs and intr_regs. To support correct cleanup perf_sample__init and perf_sample__exit functions are created and added throughout the code base. Signed-off-by: Ian Rogers <irogers@google.com> Link: https://lore.kernel.org/r/20250113194345.1537821-1-irogers@google.com Signed-off-by: Namhyung Kim <namhyung@kernel.org>
79 lines
1.8 KiB
C
79 lines
1.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <string.h>
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#include "perf_regs.h"
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#include "thread.h"
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#include "map.h"
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#include "maps.h"
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#include "event.h"
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#include "debug.h"
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#include "tests/tests.h"
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#define STACK_SIZE 8192
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static int sample_ustack(struct perf_sample *sample,
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struct thread *thread, u64 *regs)
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{
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struct stack_dump *stack = &sample->user_stack;
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struct map *map;
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unsigned long sp;
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u64 stack_size, *buf;
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buf = malloc(STACK_SIZE);
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if (!buf) {
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pr_debug("failed to allocate sample uregs data\n");
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return -1;
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}
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sp = (unsigned long) regs[PERF_REG_X86_SP];
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map = maps__find(thread__maps(thread), (u64)sp);
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if (!map) {
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pr_debug("failed to get stack map\n");
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free(buf);
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return -1;
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}
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stack_size = map__end(map) - sp;
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map__put(map);
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stack_size = stack_size > STACK_SIZE ? STACK_SIZE : stack_size;
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memcpy(buf, (void *) sp, stack_size);
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#ifdef MEMORY_SANITIZER
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/*
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* Copying the stack may copy msan poison, avoid false positives in the
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* unwinder by removing the poison here.
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*/
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__msan_unpoison(buf, stack_size);
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#endif
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stack->data = (char *) buf;
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stack->size = stack_size;
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return 0;
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}
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int test__arch_unwind_sample(struct perf_sample *sample,
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struct thread *thread)
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{
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struct regs_dump *regs = perf_sample__user_regs(sample);
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u64 *buf;
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buf = malloc(sizeof(u64) * PERF_REGS_MAX);
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if (!buf) {
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pr_debug("failed to allocate sample uregs data\n");
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return -1;
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}
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#ifdef MEMORY_SANITIZER
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/*
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* Assignments to buf in the assembly function perf_regs_load aren't
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* seen by memory sanitizer. Zero the memory to convince memory
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* sanitizer the memory is initialized.
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*/
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memset(buf, 0, sizeof(u64) * PERF_REGS_MAX);
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#endif
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perf_regs_load(buf);
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regs->abi = PERF_SAMPLE_REGS_ABI;
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regs->regs = buf;
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regs->mask = PERF_REGS_MASK;
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return sample_ustack(sample, thread, buf);
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}
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