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[34.48.67.23]) by smtp.gmail.com with UTF8SMTPSA id 00721157ae682-719532c7cc0sm26018107b3.70.2025.07.22.10.29.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Jul 2025 10:29:28 -0700 (PDT) Date: Tue, 22 Jul 2025 13:29:28 -0400 From: Willem de Bruijn To: Jason Xing , Willem de Bruijn Cc: Paul Menzel , anthony.l.nguyen@intel.com, przemyslaw.kitszel@intel.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, sdf@fomichev.me, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, mcoquelin.stm32@gmail.com, alexandre.torgue@foss.st.com, linux-stm32@st-md-mailman.stormreply.com, bpf@vger.kernel.org, intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, Jason Xing Message-ID: <687fca7852e84_2cbf622949d@willemb.c.googlers.com.notmuch> In-Reply-To: References: <20250721083343.16482-1-kerneljasonxing@gmail.com> <20250721083343.16482-2-kerneljasonxing@gmail.com> <8c9e97e4-3590-49a8-940b-717deac0078d@molgen.mpg.de> <687f9d4cf0b14_2aa7cc29443@willemb.c.googlers.com.notmuch> Subject: Re: [Intel-wired-lan] [PATCH net-next 1/2] stmmac: xsk: fix underflow of budget in zerocopy mode Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Jason Xing wrote: > On Tue, Jul 22, 2025 at 10:16=E2=80=AFPM Willem de Bruijn > wrote: > > > > Jason Xing wrote: > > > Hi Paul, > > > > > > On Mon, Jul 21, 2025 at 4:56=E2=80=AFPM Paul Menzel wrote: > > > > > > > > Dear Jason, > > > > > > > > > > > > Thank you for your patch. > > > > > > Thanks for your quick response and review :) > > > > > > > > > > > Am 21.07.25 um 10:33 schrieb Jason Xing: > > > > > From: Jason Xing > > > > > > > > > > The issue can happen when the budget number of descs are consum= ed. As > > > > > > > > Instead of =E2=80=9CThe issue=E2=80=9D, I=E2=80=99d use =E2=80=9C= An underflow =E2=80=A6=E2=80=9D. > > > > > > Will change it. > > > > > > > > > > > > long as the budget is decreased to zero, it will again go into > > > > > while (budget-- > 0) statement and get decreased by one, so the= > > > > > underflow issue can happen. It will lead to returning true wher= eas the > > > > > expected value should be false. > > > > > > > > What is =E2=80=9Cit=E2=80=9D? > > > > > > It means 'underflow of budget' behavior. > > > > A technicality, but this is (negative) overflow. > > > > Underflow is a computation that results in a value that is too small > > to be represented by the given type. > = > Interesting. Thanks for sharing this with me:) > = > I just checked the wikipedia[1] that says " Underflow can in part be > regarded as negative overflow of the exponent of the floating-point > value.". I assume this rule can also be applied in this case? I'm > hesitant to send the v3 patch tomorrow with this 'negative overflow' > term included. My point is very pedantic. I think these cases are not underflow. But it is often called that, understandably. So choose as you see fit.