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Tsirkin" To: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Jason Wang Subject: [PATCH net] ptr_ring: drop duplicated tail zeroing code Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" We have some rather subtle code around zeroing tail entries, minimizing cache bouncing. Let's put it all in one place. Doing this also reduces the text size slightly, e.g. for drivers/vhost/net.o Before: text: 15,114 bytes After: text: 15,082 bytes Signed-off-by: Michael S. Tsirkin Acked-by: Jason Wang --- Lightly tested. include/linux/ptr_ring.h | 42 +++++++++++++++++++++++----------------- 1 file changed, 24 insertions(+), 18 deletions(-) diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index 551329220e4f..a736b16859a6 100644 --- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -243,6 +243,24 @@ static inline bool ptr_ring_empty_bh(struct ptr_ring *= r) return ret; } =20 +/* Zero entries from tail to specified head. + * NB: if consumer_head can be >=3D r->size need to fixup tail later. + */ +static inline void __ptr_ring_zero_tail(struct ptr_ring *r, int consumer_h= ead) +{ + int head =3D consumer_head - 1; + + /* 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 >=3D r->consumer_tail)) + r->queue[head--] =3D NULL; + + r->consumer_tail =3D consumer_head; +} + /* Must only be called after __ptr_ring_peek returned !NULL */ static inline void __ptr_ring_discard_one(struct ptr_ring *r) { @@ -261,8 +279,7 @@ static inline void __ptr_ring_discard_one(struct ptr_ri= ng *r) /* Note: we must keep consumer_head valid at all times for __ptr_ring_emp= ty * to work correctly. */ - int consumer_head =3D r->consumer_head; - int head =3D consumer_head++; + int consumer_head =3D r->consumer_head + 1; =20 /* Once we have processed enough entries invalidate them in * the ring all at once so producer can reuse their space in the ring. @@ -270,16 +287,9 @@ static inline void __ptr_ring_discard_one(struct ptr_r= ing *r) * but helps keep the implementation simple. */ if (unlikely(consumer_head - r->consumer_tail >=3D r->batch || - consumer_head >=3D r->size)) { - /* 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 >=3D r->consumer_tail)) - r->queue[head--] =3D NULL; - r->consumer_tail =3D consumer_head; - } + consumer_head >=3D r->size)) + __ptr_ring_zero_tail(r, consumer_head); + if (unlikely(consumer_head >=3D r->size)) { consumer_head =3D 0; r->consumer_tail =3D 0; @@ -513,7 +523,6 @@ static inline void ptr_ring_unconsume(struct ptr_ring *= r, void **batch, int n, void (*destroy)(void *)) { unsigned long flags; - int head; =20 spin_lock_irqsave(&r->consumer_lock, flags); spin_lock(&r->producer_lock); @@ -525,17 +534,14 @@ static inline void ptr_ring_unconsume(struct ptr_ring= *r, void **batch, int n, * Clean out buffered entries (for simplicity). This way following code * can test entries for NULL and if not assume they are valid. */ - head =3D r->consumer_head - 1; - while (likely(head >=3D r->consumer_tail)) - r->queue[head--] =3D NULL; - r->consumer_tail =3D r->consumer_head; + __ptr_ring_zero_tail(r, r->consumer_head); =20 /* * Go over entries in batch, start moving head back and copy entries. * Stop when we run into previously unconsumed entries. */ while (n) { - head =3D r->consumer_head - 1; + int head =3D r->consumer_head - 1; if (head < 0) head =3D r->size - 1; if (r->queue[head]) { --=20 MST