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[24.6.151.244]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7ea4496690dsm278239a12.77.2024.10.09.21.59.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Oct 2024 21:59:07 -0700 (PDT) Date: Wed, 9 Oct 2024 21:59:04 -0700 From: Joe Damato To: Eric Dumazet Cc: Jakub Kicinski , netdev@vger.kernel.org, mkarsten@uwaterloo.ca, skhawaja@google.com, sdf@fomichev.me, bjorn@rivosinc.com, amritha.nambiar@intel.com, sridhar.samudrala@intel.com, willemdebruijn.kernel@gmail.com, "David S. Miller" , Paolo Abeni , Donald Hunter , Jesper Dangaard Brouer , Mina Almasry , Xuan Zhuo , open list Subject: Re: [net-next v5 4/9] netdev-genl: Dump gro_flush_timeout Message-ID: Mail-Followup-To: Joe Damato , Eric Dumazet , Jakub Kicinski , netdev@vger.kernel.org, mkarsten@uwaterloo.ca, skhawaja@google.com, sdf@fomichev.me, bjorn@rivosinc.com, amritha.nambiar@intel.com, sridhar.samudrala@intel.com, willemdebruijn.kernel@gmail.com, "David S. Miller" , Paolo Abeni , Donald Hunter , Jesper Dangaard Brouer , Mina Almasry , Xuan Zhuo , open list References: <20241009005525.13651-1-jdamato@fastly.com> <20241009005525.13651-5-jdamato@fastly.com> <20241009201440.418e21de@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Oct 10, 2024 at 06:45:11AM +0200, Eric Dumazet wrote: > On Thu, Oct 10, 2024 at 6:34 AM Joe Damato wrote: > > > > On Wed, Oct 09, 2024 at 08:14:40PM -0700, Jakub Kicinski wrote: > > > On Wed, 9 Oct 2024 00:54:58 +0000 Joe Damato wrote: > > > > + name: gro-flush-timeout > > > > + doc: The timeout, in nanoseconds, of when to trigger the NAPI > > > > + watchdog timer and schedule NAPI processing. > > > > > > You gotta respin because we reformatted the cacheline info. > > > > Yea, I figured I'd be racing with that change and would need a > > respin. > > > > I'm not sure how the queue works exactly, but it looks like I might > > also be racing with another change [1], I think. > > > > I think I'm just over 24hr and could respin and resend now, but > > should I wait longer in case [1] is merged before you see my > > respin? > > I would avoid the rtnl_lock() addition in "netdev-genl: Support > setting per-NAPI config values" > before re-sending ? OK. > > > > Just trying to figure out how to get the fewest number of respins > > possible ;) > > > > > So while at it perhaps throw in a sentence here about the GRO effects? > > > The initial use of GRO flush timeout was to hold incomplete GRO > > > super-frames in the GRO engine across NAPI cycles. > > > > From my reading of the code, if the timeout is non-zero, then > > napi_gro_flush will flush only "old" super-frames in > > napi_complete_done. > > > > If that's accurate (and maybe I missed something?), then how about: > > > > doc: The timeout, in nanoseconds, of when to trigger the NAPI > > watchdog timer which schedules NAPI processing. Additionally, a > > non-zero value will also prevent GRO from flushing recent > > super-frames at the end of a NAPI cycle. This may add receive > > latency in exchange for reducing the number of frames processed > > by the network stack. > > Note that linux TCP always has a PSH flag at the end of each TSO packet, > so the latency increase is only possible in presence of tail drop, > if the last MSS (with the PSH) was dropped. Would you like me to note that in the doc, as well?