Messages in this thread | | | Date | Mon, 13 Apr 2015 23:49:34 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v14 for 4.1] sys_membarrier(): system-wide memory barrier (x86) |
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On Mon, 13 Apr 2015, Mathieu Desnoyers wrote:
> [ Andrew, can you take this for the 4.1 merge window ? ]
You probably mean 4.2, right?
This fails the basic test for exposure in linux-next, adds syscalls without the explicit ack of any x86 maintainer and exposes a user space ABI with a magic undocumented flags argument.
> This patch only adds the system call to x86.
So the changes to
> include/uapi/asm-generic/unistd.h | 4 +-
are just cosmetic, right?
> +/* System call membarrier "flags" argument. */ > +enum { > + /* > + * Query whether the rest of the specified flags are supported, > + * without performing synchronization. > + */
Docbook has support for enums.
> + MEMBARRIER_QUERY = (1 << 31), > +};
Why is this an anonymous enum?
> +#ifdef CONFIG_SMP
So documentation is SMP only, right?
> +/*
Docbook comments start with "/**"
> + * sys_membarrier - issue memory barrier on all running threads > + * @flags: MEMBARRIER_QUERY: > + * Query whether the rest of the specified flags are supported, > + * without performing synchronization.
@flags: Explain what this is for, not what a particular implemented value is used for. The values should be proper documented in the enum
Why is this an int and not a named enum?
Why is this named flags and not given a descriptive name? If I understand your changelog correctly you want to implement other synchronization modes than the current synchronize_sched. So mode might be a proper name.
Why is MEMBARRIER_QUERY not a proper operation mode and simply returns the supported modes instead of doing it backwards and asking whether a specific value is supported?
> + * On uniprocessor systems, this system call simply returns 0 after > + * validating the arguments, so user-space knows it is implemented.
And the exact point of knowing this is?
> + */ > +SYSCALL_DEFINE1(membarrier, int, flags) > +{ > + int retval; > + > + retval = membarrier_validate_flags(flags); > + if (retval) > + goto end; > + if (unlikely(flags & MEMBARRIER_QUERY) || num_online_cpus() == 1) > + goto end;
So why not doing the obvious?
enum modes { QUERY = 0, FULL_SYNC = 1 << 0, };
#define IMPLEMENTED_MODES (FULL_SYNC)
switch (mode) { case FULL_SYNC: synchronize_sched_on_smp(); return 0; case QUERY: return IMPLEMENTED_MODES; } return -EINVAL;
And later on you do
enum modes { QUERY = 0, FULL_SYNC = 1 << 0, + MAGIC_SYNC = 1 << 1, };
-#define IMPLEMENTED_MODES (FULL_SYNC) +#define IMPLEMENTED_MODES (FULL_SYNC | MAGIC_SYNC)
All you need to make sure is that any mode is a power of 2.
Hmm?
Thanks,
tglx
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