On Thu, 2015-03-12 at 11:58 +0100, Ingo Molnar wrote:
> > > +/**
> > > + * pcommit_sfence() - persistent commit and fence
> > > + *
> > > + * The pcommit instruction ensures that data that has been flushed from
> > > the
> > > + * processor's cache hierarchy with clwb, clflushopt or clflush is
> > > accepted to
> > > + * memory and is durable on the DIMM. The primary use case for this is
> > > + * persistent memory.
>
> Please capitalize canonical instruction names like the CPU makers do,
> so that they stand out better in free flowing English text, i.e.
> something like:
>
> *
> * The PCOMMIT instruction ensures that data that has been flushed from the
> * processor's cache hierarchy with CLWB, CLFLUSHOPT or CLFLUSH is accepted to
> * memory and is durable on the DIMM. The primary use case for this is
> * persistent memory.
Sure, will do.
> > > + * void flush_and_commit_buffer(void *vaddr, unsigned int size)
> > > + * {
> > > + * unsigned long clflush_mask = boot_cpu_data.x86_clflush_size -
> > > 1;
> > > + * char *vend = (char *)vaddr + size;
>
> So here we cast vaddr to (char *) - which is unnecessary, as 'void *'
> has byte granular pointer arithmetics.
>
> And 'vend' should be void *' to begin with, to match the type
> of 'vaddr'.
The original version, copied in part from clflush_cache_range, did do
everything with void* pointers. I changed it to use char* pointers based on
feedback from hpa. :)
It seems like both have arguments for them. Char pointer arithmetic has the
advantage that its behavior is standard in C, so it's not specific to gcc. I
agree that void* has the advantage that it fits more naturally with the types
of the parameters passed in, requiring no casting.
I honestly don't feel strongly either way - please let me know what you guys
prefer in the x86 arch code.
> > > + * for (p = (char *)((unsigned long)vaddr & ~clflush_mask);
> > > + * p < vend; p += boot_cpu_data.x86_clflush_size)
> > > + * clwb(p);
> > > + *
> > > + * // sfence to order clwb/clflushopt/clflush cache flushes
> > > + * // mfence via mb() also works
>
> Yeah so this isn't a C++ kernel, thank all the 3000+ gods and other
> supreme beings worshipped on this planet!
Yep. C++ style // comments are happily accepted by gcc in C code, though, and
this was my attempt to get around the fact that /* */ style comments can't be
nested. I couldn't think of a more elegant way of having code + comments in a
kerneldoc comment. I agree that if this code were ever to be pulled out and
used, the comment style would need to be corrected to be the standard kernel
style.
> Also please put 'vaddr' into single quotes, to make the parameter name
> stand out better in written text:
>
> > > + * After this function completes the data pointed to by 'vaddr' has been
Sure.
Thanks,
- Ross
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