28/10/2022 08:41, Morten Brørup: > Add __rte_cache_aligned to the objs array. > > It makes no difference in the general case, but if get/put operations are > always 32 objects, it will reduce the number of memory (or last level > cache) accesses from five to four 64 B cache lines for every get/put > operation. > > For readability reasons, an example using 16 objects follows: > > Currently, with 16 objects (128B), we access to 3 > cache lines: > > ┌────────┐ > │len │ > cache │********│--- > line0 │********│ ^ > │********│ | > ├────────┤ | 16 objects > │********│ | 128B > cache │********│ | > line1 │********│ | > │********│ | > ├────────┤ | > │********│_v_ > cache │ │ > line2 │ │ > │ │ > └────────┘ > > With the alignment, it is also 3 cache lines: > > ┌────────┐ > │len │ > cache │ │ > line0 │ │ > │ │ > ├────────┤--- > │********│ ^ > cache │********│ | > line1 │********│ | > │********│ | > ├────────┤ | 16 objects > │********│ | 128B > cache │********│ | > line2 │********│ | > │********│ v > └────────┘--- > > However, accessing the objects at the bottom of the mempool cache is a > special case, where cache line0 is also used for objects. > > Consider the next burst (and any following bursts): > > Current: > ┌────────┐ > │len │ > cache │ │ > line0 │ │ > │ │ > ├────────┤ > │ │ > cache │ │ > line1 │ │ > │ │ > ├────────┤ > │ │ > cache │********│--- > line2 │********│ ^ > │********│ | > ├────────┤ | 16 objects > │********│ | 128B > cache │********│ | > line3 │********│ | > │********│ | > ├────────┤ | > │********│_v_ > cache │ │ > line4 │ │ > │ │ > └────────┘ > 4 cache lines touched, incl. line0 for len. > > With the proposed alignment: > ┌────────┐ > │len │ > cache │ │ > line0 │ │ > │ │ > ├────────┤ > │ │ > cache │ │ > line1 │ │ > │ │ > ├────────┤ > │ │ > cache │ │ > line2 │ │ > │ │ > ├────────┤ > │********│--- > cache │********│ ^ > line3 │********│ | > │********│ | 16 objects > ├────────┤ | 128B > │********│ | > cache │********│ | > line4 │********│ | > │********│_v_ > └────────┘ > Only 3 cache lines touched, incl. line0 for len. > > Credits go to Olivier Matz for the nice ASCII graphics. > > v4: > * No changes. Added reviewed- and acked-by tags. > v3: > * No changes. Made part of a series. > v2: > * No such version. > > Signed-off-by: Morten Brørup <m...@smartsharesystems.com> > Reviewed-by: Andrew Rybchenko <andrew.rybche...@oktetlabs.ru> > Acked-by: Olivier Matz <olivier.m...@6wind.com>
Applied only this first patch, thanks. The second patch needs more time.
