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Tsirkin" To: linux-kernel@vger.kernel.org, netdev@vger.kernel.org Cc: Jason Wang Subject: [PATCH net-next] ptr_ring: __ptr_ring_zero_tail micro optimization Message-ID: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent __ptr_ring_zero_tail currently does the - 1 operation twice: - during initialization of head - at each loop iteration Let's just do it in one place, all we need to do is adjust the loop condition. this is better: - a slightly clearer logic with less duplication - uses prefix -- we don't need to save the old value - one less - 1 operation - for example, when ring is empty we now don't do - 1 at all, existing code does it once Text size shrinks from 15081 to 15050 bytes. Signed-off-by: Michael S. Tsirkin --- include/linux/ptr_ring.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index 4d014b6c4206..ba90c0e6ce70 100644 --- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -248,15 +248,15 @@ static inline bool ptr_ring_empty_bh(struct ptr_ring *r) */ static inline void __ptr_ring_zero_tail(struct ptr_ring *r, int consumer_head) { - int head = consumer_head - 1; + int head = consumer_head; /* Zero out entries in the reverse order: this way we touch the * cache line that producer might currently be reading the last; * producer won't make progress and touch other cache lines * besides the first one until we write out all entries. */ - while (likely(head >= r->consumer_tail)) - r->queue[head--] = NULL; + while (likely(head > r->consumer_tail)) + r->queue[--head] = NULL; r->consumer_tail = consumer_head; } -- MST