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[34.145.139.141]) by smtp.gmail.com with UTF8SMTPSA id d75a77b69052e-4b48f652814sm1143791cf.12.2025.09.02.14.13.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Sep 2025 14:13:17 -0700 (PDT) Date: Tue, 02 Sep 2025 17:13:17 -0400 From: Willem de Bruijn To: Simon Schippers , willemdebruijn.kernel@gmail.com, jasowang@redhat.com, mst@redhat.com, eperezma@redhat.com, stephen@networkplumber.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org Cc: Simon Schippers , Tim Gebauer Message-ID: In-Reply-To: <20250902080957.47265-2-simon.schippers@tu-dortmund.de> References: <20250902080957.47265-1-simon.schippers@tu-dortmund.de> <20250902080957.47265-2-simon.schippers@tu-dortmund.de> Subject: Re: [PATCH 1/4] ptr_ring_spare: Helper to check if spare capacity of size cnt is available Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Simon Schippers wrote: > The implementation is inspired by ptr_ring_empty. > > Co-developed-by: Tim Gebauer > Signed-off-by: Tim Gebauer > Signed-off-by: Simon Schippers > --- > include/linux/ptr_ring.h | 71 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 71 insertions(+) > > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h > index 551329220e4f..6b8cfaecf478 100644 > --- a/include/linux/ptr_ring.h > +++ b/include/linux/ptr_ring.h > @@ -243,6 +243,77 @@ static inline bool ptr_ring_empty_bh(struct ptr_ring *r) > return ret; > } > > +/* > + * Check if a spare capacity of cnt is available without taking any locks. > + * > + * If cnt==0 or cnt > r->size it acts the same as __ptr_ring_empty. cnt >= r->size? > + * > + * The same requirements apply as described for __ptr_ring_empty. > + */ > +static inline bool __ptr_ring_spare(struct ptr_ring *r, int cnt) > +{ > + int size = r->size; > + int to_check; > + > + if (unlikely(!size || cnt < 0)) > + return true; Does !size ever happen. Also no need for preconditions for trivial errors that never happen, like passing negative values. Or prefer an unsigned type. > + > + if (cnt > size) > + cnt = 0; > + > + to_check = READ_ONCE(r->consumer_head) - cnt; > + > + if (to_check < 0) > + to_check += size; > + > + return !r->queue[to_check]; > +} > + > +static inline bool ptr_ring_spare(struct ptr_ring *r, int cnt) > +{ > + bool ret; > + > + spin_lock(&r->consumer_lock); > + ret = __ptr_ring_spare(r, cnt); > + spin_unlock(&r->consumer_lock); > + > + return ret; > +} > + > +static inline bool ptr_ring_spare_irq(struct ptr_ring *r, int cnt) > +{ > + bool ret; > + > + spin_lock_irq(&r->consumer_lock); > + ret = __ptr_ring_spare(r, cnt); > + spin_unlock_irq(&r->consumer_lock); > + > + return ret; > +} > + > +static inline bool ptr_ring_spare_any(struct ptr_ring *r, int cnt) > +{ > + unsigned long flags; > + bool ret; > + > + spin_lock_irqsave(&r->consumer_lock, flags); > + ret = __ptr_ring_spare(r, cnt); > + spin_unlock_irqrestore(&r->consumer_lock, flags); > + > + return ret; > +} > + > +static inline bool ptr_ring_spare_bh(struct ptr_ring *r, int cnt) > +{ > + bool ret; > + > + spin_lock_bh(&r->consumer_lock); > + ret = __ptr_ring_spare(r, cnt); > + spin_unlock_bh(&r->consumer_lock); > + > + return ret; > +} Please only introduce the variants actually used.