Re: [Qemu-devel] Re: [PATCH 12/15] Support 1T segments on ppc

[David Gibson]

On Sun, Feb 13, 2011 at 01:37:12PM +0100, Alexander Graf wrote:
> On 13.02.2011, at 10:34, David Gibson wrote:
> > On Sat, Feb 12, 2011 at 04:57:39PM +0100, Alexander Graf wrote:
> >> On 12.02.2011, at 15:54, David Gibson wrote:
> > [snip]
> >>> +    if (rb & (0x1000 - env->slb_nr))
> >> 
> >> Braces...
> > 
> > Oops, yeah.  These later patches in the series I haven't really
> > audited for coding style adequately yet.  I'll fix these before the
> > next version.
> > 
> > [snip]
> >>> +         return -1; /* 1T segment on MMU that doesn't support it */
> >>> + 
> >>> +    /* We stuff a copy of the B field into slb->esid to simplify
> >>> +     * lookup later */
> >>> +    slb->esid = (rb & (SLB_ESID_ESID | SLB_ESID_V)) |
> >>> +        (rs >> SLB_VSID_SSIZE_SHIFT);
> >> 
> >> Wouldn't it be easier to add another field?
> > 
> > Easier for what?  The reason I put these bits in here is that the rest
> > of the things slb_lookup() needs to scan for are all in the esid
> > field, so putting B in there means slb_lookup() needs only one
> > comparison per-slot, per segment size.
> 
> Hrm - but it also needs random & ~3 masking in other code which is
> very unpretty. Comparing two numbers really shouldn't hurt
> performance too much, but makes the code better maintainable.

Well, it's only one place.  But fair enough, I'll avoid this hack in
the next version.

> struct slb_entry {
>     uint64_t esid;
>     uint64_t vsid;
>     int b;
> }
> 
> or so :).

Actually, we don't even need that.  The B field is already in
slb->vsid.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson