Dynamic pcpu, arm, mips, powerpc, sun, etc. help needed

[Jeff Roberson]

On Wed, 17 Jun 2009, M. Warner Losh wrote:

> In message: <alpine.BSF.2.00.0906171231540.1025 at desktop>
>            Jeff Roberson <jroberson at jroberson.net> writes:
> :
> : On Tue, 9 Jun 2009, Peter Grehan wrote:
> :
> : >> As for sparc64 allocating the storage for the dynamic area
> : >> from end probably isn't a good idea as the pmap code assumes
> : >> that the range from KERNBASE to end is covered by the pages
> : >> allocated by and locked into the TLB for the kernel by the
> : >> loader
> : >
> : > Ditto for ppc. It's possible to get the additional space from within or
> : > after return from pmap_bootstrap() (like thread0's kstack, or the msgbuf).
> :
> : http://people.freebsd.org/~jeff/dpcpu.diff
> :
> : I have updated this patch based on feedback relating to various
> : architectures md code.  I tried to model most architectures after the way
> : msgbuf memory was taken.  I have no capacity to test anything other than
> : i386 and amd64.  ARM is reported to work with one minor diff.  Apparently
> : sparc64 worked with the earlier diff but this should be cleaner.  If
> : anyone can report back on sparc64, mips, or powerpc, I'd appreciate it.
>
>
> I don't understand this part of the patch:
>
> Index: mips/mips/mp_machdep.c
> ===================================================================
> --- mips/mips/mp_machdep.c	(revision 194275)
> +++ mips/mips/mp_machdep.c	(working copy)
> @@ -224,12 +224,15 @@ static int
> smp_start_secondary(int cpuid)
> {
> 	struct pcpu *pcpu;
> +	void *dpcpu;
> 	int i;
>
> 	if (bootverbose)
> 		printf("smp_start_secondary: starting cpu %d\n", cpuid);
>
> +	dpcpu = (void *)kmem_alloc(kernel_map, DPCPU_SIZE);
> 	pcpu_init(&__pcpu[cpuid], cpuid, sizeof(struct pcpu));
> +	dpcpu_init(dpcpu, cpuid);
>
> 	if (bootverbose)
> 		printf("smp_start_secondary: cpu %d started\n", cpuid);
>
> So were adding a dynamic per-cpu area, in addition to the fixed part?

Yes, the fixed part is for legacy and very frequently accessed items that 
need fixed addresses.  The dynamic area is for convenience and is slightly 
more expensive to access.  It also has addresses that are not resolved 
until link time.

The fixed area uses a static structure with a size that is known at 
compile time.  The dynamic part is only known at link time and so must be 
allocated seperately.

Jeff

>
> Warner
>