Re: [PATCH 2/4] KVM: Avoid checking huge page mappings inget_dirty_log()

[Takuya Yoshikawa]

Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx> wrote:

> Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx> wrote:
> 
> > +	while (mask) {
> > +		rmapp = &slot->rmap[gfn_offset + __ffs(mask)];
> > +		__rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);
> >  
> > -	return write_protected;
> > +		/* clear the first set bit */
> > +		mask &= mask - 1;
> > +	}
> >  }
> 
> while (mask) {
> 	fsbit = __ffs(mask);
> 	gfn_offset += fsbit;
> 	mask >>= fsbit + 1;
> 
> 	rmapp = &slot->rmap[gfn_offset];
> 	__rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);
> }
> 
> Seems to be better: BSF friendly.

I was wrong.

"and < shift" and bsf did not show any difference for this kind of loop
on my box.  So we should keep the original implementation.

	Takuya
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