romenskiy2012/jemalloc
1
0
Fork 0
mirror of https://github.com/jemalloc/jemalloc.git synced 2026-07-13 04:07:23 +03:00
Code Issues Projects Releases Packages Wiki Activity

Fix malloc_getcpu on macOS to read the current CPU number correctly

Browse source 
The Apple branch read the CPU number from the low 3 bits of `tpidrro_el0`.
That layout no longer holds on Apple Silicon: those bits read back as 0, so
`malloc_getcpu` returned 0 for every thread. `percpu_arena` then funneled all
allocations into arena 0, or was disabled outright at init.

Read the CPU number the same way as libplatform's `_os_cpu_number`: the low 12
bits of `tpidr_el0` on arm64, or of the IDT base (via `sidt`) on x86. Also move
the Apple branch ahead of the `rdtscp` one so Apple x86 uses `sidt` rather than
`rdtscp`, whose `ecx` is not the CPU id under XNU.
https://github.com/apple-oss-distributions/xnu/blob/main/libsyscall/os/tsd.h

Verified on a 12-CPU M2 Pro: with `percpu_arena:percpu`, `opt.percpu_arena` now
stays `percpu` and `thread.arena` spreads across all 12 arenas {0..11}; the old
code collapsed every thread onto arena 0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Raúl Marín 2026-07-07 16:47:54 +02:00 • committed by Guangli Dai
parent b859093d28
commit 5aabbc87bf
1 changed files with 16 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

21
include/jemalloc/internal/jemalloc_internal_inlines_a.h
View file

@ -18,15 +18,26 @@ malloc_getcpu(void) {
return GetCurrentProcessorNumber();
#elif defined(JEMALLOC_HAVE_SCHED_GETCPU)
return (malloc_cpuid_t)sched_getcpu();
#elif defined(__APPLE__)
/* No sched_getcpu() on macOS; read the CPU number like _os_cpu_number(), see
* https://github.com/apple-oss-distributions/xnu/blob/main/libsyscall/os/tsd.h
* (it is no longer in tpidrro_el0's low bits on Apple Silicon). */
# if defined(__aarch64__)
uint64_t cpu;
__asm__ __volatile__("mrs %0, tpidr_el0" : "=r"(cpu));
return (malloc_cpuid_t)(cpu & 0xfff);
# elif defined(__x86_64__) || defined(__i386__)
struct { uintptr_t p1, p2; } idtr;
__asm__ __volatile__("sidt %0" : "=m"(idtr));
return (malloc_cpuid_t)(idtr.p1 & 0xfff);
# else
not_reached();
return -1;
# endif
#elif defined(JEMALLOC_HAVE_RDTSCP)
unsigned int ecx;
asm volatile("rdtscp" : "=c"(ecx)::"eax", "edx");
return (malloc_cpuid_t)(ecx & 0xfff);
#elif defined(__aarch64__) && defined(__APPLE__)
/* Other oses most likely use tpidr_el0 instead */
uintptr_t c;
asm volatile("mrs %x0, tpidrro_el0" : "=r"(c)::"memory");
return (malloc_cpuid_t)(c & (1 << 3) - 1);
#else
not_reached();
return -1;