forked from Minki/linux
2c0b8a7578
Actually, on 386, cmpxchg and cmpxchg_local fall back on cmpxchg_386_u8/16/32: it disables interruptions around non atomic updates to mimic the cmpxchg behavior. The comment: /* Poor man's cmpxchg for 386. Unsuitable for SMP */ already present in cmpxchg_386_u32 tells much about how this cmpxchg implementation should not be used in a SMP context. However, the cmpxchg_local can perfectly use this fallback, since it only needs to be atomic wrt the local cpu. This patch adds a cmpxchg_486_u64 and uses it as a fallback for cmpxchg64 and cmpxchg64_local on 80386 and 80486. Q: but why is it called cmpxchg_486 when the other functions are called A: Because the standard cmpxchg is missing only on 386, but cmpxchg8b is missing both on 386 and 486. Citing Intel's Instruction set reference: cmpxchg: This instruction is not supported on Intel processors earlier than the Intel486 processors. cmpxchg8b: This instruction encoding is not supported on Intel processors earlier than the Pentium processors. Q: What's the reason to have cmpxchg64_local on 32 bit architectures? Without that need all this would just be a few simple defines. A: cmpxchg64_local on 32 bits architectures takes unsigned long long parameters, but cmpxchg_local only takes longs. Since we have cmpxchg8b to execute a 8 byte cmpxchg atomically on pentium and +, it makes sense to provide a flavor of cmpxchg and cmpxchg_local using this instruction. Also, for 32 bits architectures lacking the 64 bits atomic cmpxchg, it makes sense _not_ to define cmpxchg64 while cmpxchg could still be available. Moreover, the fallback for cmpxchg8b on i386 for 386 and 486 is a However, cmpxchg64_local will be emulated by disabling interrupts on all architectures where it is not supported atomically. Therefore, we *could* turn cmpxchg64_local into a cmpxchg_local, but it would make the 386/486 fallbacks ugly, make its design different from cmpxchg/cmpxchg64 (which really depends on atomic operations and cannot be emulated) and require the __cmpxchg_local to be expressed as a macro rather than an inline function so the parameters would not be fixed to unsigned long long in every case. So I think cmpxchg64_local makes sense there, but I am open to suggestions. Q: Are there any callers? A: I am actually using it in LTTng in my timestamping code. I use it to work around CPUs with asynchronous TSCs. I need to update 64 bits values atomically on this 32 bits architecture. Changelog: - Ran though checkpatch. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: Andi Kleen <ak@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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| .. | ||
| acpi | ||
| cpu | ||
| .gitignore | ||
| alternative.c | ||
| aperture_64.c | ||
| apic_32.c | ||
| apic_64.c | ||
| apm_32.c | ||
| asm-offsets_32.c | ||
| asm-offsets_64.c | ||
| asm-offsets.c | ||
| audit_64.c | ||
| bootflag.c | ||
| bugs_64.c | ||
| cpuid.c | ||
| crash_dump_32.c | ||
| crash_dump_64.c | ||
| crash.c | ||
| doublefault_32.c | ||
| e820_32.c | ||
| e820_64.c | ||
| early_printk.c | ||
| early-quirks.c | ||
| efi_32.c | ||
| efi_stub_32.S | ||
| entry_32.S | ||
| entry_64.S | ||
| genapic_64.c | ||
| genapic_flat_64.c | ||
| geode_32.c | ||
| head64.c | ||
| head_32.S | ||
| head_64.S | ||
| hpet.c | ||
| i386_ksyms_32.c | ||
| i387_32.c | ||
| i387_64.c | ||
| i8237.c | ||
| i8253.c | ||
| i8259_32.c | ||
| i8259_64.c | ||
| init_task.c | ||
| io_apic_32.c | ||
| io_apic_64.c | ||
| io_delay.c | ||
| ioport_32.c | ||
| ioport_64.c | ||
| irq_32.c | ||
| irq_64.c | ||
| k8.c | ||
| kprobes_32.c | ||
| kprobes_64.c | ||
| ldt.c | ||
| machine_kexec_32.c | ||
| machine_kexec_64.c | ||
| Makefile | ||
| Makefile_32 | ||
| Makefile_64 | ||
| mca_32.c | ||
| mfgpt_32.c | ||
| microcode.c | ||
| module_32.c | ||
| module_64.c | ||
| mpparse_32.c | ||
| mpparse_64.c | ||
| msr.c | ||
| nmi_32.c | ||
| nmi_64.c | ||
| numaq_32.c | ||
| paravirt_32.c | ||
| pci-calgary_64.c | ||
| pci-dma_32.c | ||
| pci-dma_64.c | ||
| pci-gart_64.c | ||
| pci-nommu_64.c | ||
| pci-swiotlb_64.c | ||
| pcspeaker.c | ||
| pmtimer_64.c | ||
| process_32.c | ||
| process_64.c | ||
| ptrace_32.c | ||
| ptrace_64.c | ||
| quirks.c | ||
| reboot_32.c | ||
| reboot_64.c | ||
| reboot_fixups_32.c | ||
| relocate_kernel_32.S | ||
| relocate_kernel_64.S | ||
| rtc.c | ||
| scx200_32.c | ||
| setup64.c | ||
| setup_32.c | ||
| setup_64.c | ||
| sigframe_32.h | ||
| signal_32.c | ||
| signal_64.c | ||
| smp_32.c | ||
| smp_64.c | ||
| smpboot_32.c | ||
| smpboot_64.c | ||
| smpcommon_32.c | ||
| srat_32.c | ||
| stacktrace.c | ||
| summit_32.c | ||
| suspend_64.c | ||
| suspend_asm_64.S | ||
| sys_i386_32.c | ||
| sys_x86_64.c | ||
| syscall_64.c | ||
| syscall_table_32.S | ||
| tce_64.c | ||
| time_32.c | ||
| time_64.c | ||
| tls.c | ||
| topology.c | ||
| trampoline_32.S | ||
| trampoline_64.S | ||
| traps_32.c | ||
| traps_64.c | ||
| tsc_32.c | ||
| tsc_64.c | ||
| tsc_sync.c | ||
| verify_cpu_64.S | ||
| vm86_32.c | ||
| vmi_32.c | ||
| vmiclock_32.c | ||
| vmlinux_32.lds.S | ||
| vmlinux_64.lds.S | ||
| vmlinux.lds.S | ||
| vsmp_64.c | ||
| vsyscall_64.c | ||
| x8664_ksyms_64.c | ||