----- Original Message -----
> On Fri, 17 Apr 2015, Mathieu Desnoyers wrote:
> > +/**
> > + * enum membarrier_cmd - membarrier system call command
> > + *
>
> * @MEMBARRIER_CMD_QUERY: Explanatory blurb......
>
> Hint: Create a kerneldoc document and build it.
Oops, fixed, and figured out how to build it. Next version
should be ok.
>
> > + * Command to be passed to the membarrier system call.
>
> Please epxlain, that the commands need to be a single bit each.
OK
>
> > +config MEMBARRIER
> > + bool "Enable membarrier() system call" if EXPERT
> > + default y
> > + depends on SMP
> > + help
> > + Enable the membarrier() system call that allows issuing memory
> > + barriers across all running threads, which can be used to distribute
> > + the cost of user-space memory barriers asymmetrically by transforming
> > + pairs of memory barriers into pairs consisting of membarrier() and a
> > + compiler barrier.
> > +
> > + If unsure, say Y.
>
> Is it really worth to make this configurable?
Josh Triplett asked for it to be made configurable. I don't have any strong
opinion one way or the other.
>
> > +/**
> > + * sys_membarrier - issue memory barriers on a set of threads
> > + * @cmd: MEMBARRIER_CMD_QUERY:
> > + * Query the set of supported commands. It returns a bitmask
> > of
> > + * supported commands.
> > + * MEMBARRIER_CMD_SHARED:
> > + * Execute a memory barrier on all running threads. Upon
> > + * return from system call, the caller thread is ensured that
> > + * all running threads have passed through a state where all
> > + * memory accesses to user-space addresses match program order
> > + * between entry to and return from the system call
> > (non-running
> > + * threads are de facto in such a state). This covers threads
> > + * from all processes running on the system. This command
> > + * returns 0.
>
> I think the explanation for the commands should be in the enum
> documentation. This here should explain that @cmd takes command values
> defined in the enum.
OK
>
> > +SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
> > +{
> > + switch (cmd) {
> > + case MEMBARRIER_CMD_QUERY:
> > + return MEMBARRIER_CMD_BITMASK;
> > + case MEMBARRIER_CMD_SHARED:
> > + if (num_online_cpus() > 1)
> > + synchronize_sched();
> > + return 0;
> > + default:
> > + return -EINVAL;
> > + }
> > +}
>
> This looks way cleaner now :)
Much smaller too :)
Thanks,
Mathieu
>
> Thanks,
>
> tglx
>
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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