On Thu, Oct 12, 2023 at 07:25:11AM +0200, Christoph Hellwig wrote:
> On Wed, Oct 11, 2023 at 11:06:14AM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@xxxxxxxxxx>
> >
> > Avoid the costs of integer division (32-bit and 64-bit) if the realtime
> > extent size is a power of two.
>
> Looks good:
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>
> Do you have any data on how common non-power of two rtext sizes are?
> Might it be worth to add unlikely annotations?
I don't really know about the historical uses. There might be old
filesystems out there with a non-power-of-2 raid stripe size that are
set up for full stripe allocations for speed.
We (oracle) are interested in using rt for PMD allocations on pmem/cxl
devices and atomic writes on scsi/nvme devices. Both of those cases
will only ever use powers of 2.
I'll add some if-test annotations and we'll see if anyone notices. ;)
--D
> > @@ -11,6 +11,9 @@ xfs_rtx_to_rtb(
> > struct xfs_mount *mp,
> > xfs_rtxnum_t rtx)
> > {
> > + if (mp->m_rtxblklog >= 0)
> > + return rtx << mp->m_rtxblklog;
> > +
> > return rtx * mp->m_sb.sb_rextsize;
>
> i.e.
>
> if (unlikely(mp->m_rtxblklog == ‐1))
> return rtx * mp->m_sb.sb_rextsize;
> return rtx << mp->m_rtxblklog;
>
