On Fri, Aug 30, 2019 at 04:43:33PM +0800, Gao Xiang wrote:
> Hi Dan,
>
> On Fri, Aug 30, 2019 at 11:34:45AM +0300, Dan Carpenter wrote:
> > On Fri, Aug 30, 2019 at 12:04:41AM +0800, Gao Xiang wrote:
> > > Anyway, I'm fine to delete them all if you like, but I think majority of
> > > these
> > > are meaningful.
> > >
> > > data.c- /* page is already locked */
> > > data.c- DBG_BUGON(PageUptodate(page));
> > > data.c-
> > > data.c: if (unlikely(err))
> > > data.c- SetPageError(page);
> > > data.c- else
> > > data.c- SetPageUptodate(page);
> >
> > If we cared about speed here then we would delete the DBG_BUGON() check
> > because that's going to be expensive. The likely/unlikely annotations
> > should be used in places a reasonable person thinks it will make a
> > difference to benchmarks.
>
> DBG_BUGON will be a no-op ((void)x) in non-debugging mode,
It expands to:
((void)PageUptodate(page));
Calling PageUptodate() doesn't do anything, but it isn't free. The
time it takes to do that function call completely negates any speed up
from using likely/unlikely.
I'm really not trying to be a jerk...
regards,
dan carpenter
