From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: passt.top; dkim=pass (2048-bit key; secure) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=202602 header.b=OZXSqGLp; dkim-atps=neutral Received: from mail.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by passt.top (Postfix) with ESMTPS id 375DE5A026D for ; Thu, 04 Jun 2026 07:26:48 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202602; t=1780550804; bh=eejv8MBrOPdlSPmxIRGZkZIxAhV4jchzbJLVR1x3xCY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OZXSqGLp6LUASbpfAvUlXT6mOcr/+mFLFHA7+zCXILzRl9bWZGH4u4W1Y373v2PK8 Tg3ARlwklEULtzkdIvkA98MLdmWAb+iwg7rfB6/NmiKxdj5HjubcBs79oWiiQTLMHG m7vsVOd/SU3IOx9d2eEblyqUDaDBT17mOGMzlcM2DyJavtL9LTPLo8+/mPj5n4iSns QgFkltDrNtZ5fSbkn6Vj9ArG86iAgBeYzUgJ4j8+YHh3mNF7wD6jrTUbzzo5apcocK ryij19Ql47Do8DcoLwujON/tmq46fzgIOJYfcRYy2TcUARv8BCHTbPTqC2vu9StAfp hku+rCDga6/zA== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4gWCjc5BQ2z4wxF; Thu, 04 Jun 2026 15:26:44 +1000 (AEST) Date: Thu, 4 Jun 2026 15:14:54 +1000 From: David Gibson To: Stefano Brivio Subject: Re: [PATCH 7/8] tcp_splice: Remove questionable "optimisation" of pending bytes tracking Message-ID: References: <20260528050213.679685-1-david@gibson.dropbear.id.au> <20260528050213.679685-8-david@gibson.dropbear.id.au> <20260604064142.5abdaced@elisabeth> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="swunxSV8odEKHzY1" Content-Disposition: inline In-Reply-To: <20260604064142.5abdaced@elisabeth> Message-ID-Hash: BKXVDXANURQRKZLCOBJBAKLBWM3G2FU6 X-Message-ID-Hash: BKXVDXANURQRKZLCOBJBAKLBWM3G2FU6 X-MailFrom: dgibson@gandalf.ozlabs.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --swunxSV8odEKHzY1 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jun 04, 2026 at 06:41:43AM +0200, Stefano Brivio wrote: > On Thu, 28 May 2026 15:02:12 +1000 > David Gibson wrote: >=20 > > We have a special path that avoids updating conn->pending when the amou= nts > > read and written are equal. This has a conceptual complexity cost, in > > particular, it means that conn->pending[] is not accurate to its normal > > meaning for a section of the loop body. > >=20 > > conn->pending[] shares a cacheline with conn->pipe[] and conn->s[], so = it's > > almost certainly cache-hot. It's questionable that avoiding the update > > of pending even outweighs the extra conditional branch, let alone saves > > anything of significance. Remove it. >=20 > I added this when we still had 64-bit counters, that is, two weeks > before commit 37c228ada88b ("tap, tcp, udp, icmp: Cut down on some > oversized buffers"), but now, as you point out, it doesn't make sense any= more. Ah, that makes some sense. --=20 David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson --swunxSV8odEKHzY1 Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmohCc0ACgkQzQJF27ox 2GehtQ//a3qzV6N9bd/5+Ek6VXJhFspyg8zrdtnBs0Jie2wk9C+UZTT088ueF1oY 03ccPJLwEXzABry7gn38JUitF8jASLDqLZv8N0jQ16YZuLUSxxBbdUGLTv0zwQY7 gyzpxrNQqnRN33VNVi5QsQvNJADv1vRhvOnUgdwodDDLImA7EPpbExR29xgQFoyM YZYTT7lMYqf461qY93pInmCp4HLHVVd+Ret+aVU9Vm1z9gt6tcD7ASiTxVa7gTkd FYRuglJ0aqb3JPMPXHsJvt6pXZE2WrTwxu4KeE+1fQnWFTgiL3J26vL/dELlJ3d3 WD+ZebS0SQRVBDo44+kLbmwY/f32YAqOURtGOILzlyg0MqaRzGE77qKhqWLd91/u /YtuYPbhkOVdf+UgR5NcxdRur7GsifnH4ZQtlH7UMsDUkZbfWd70D7F4ZOI6n9uE 6bGLu7MPjIKDtBxtAwtxk2pOWOi9V9JH5iMEg1XXKl+0KDhTVO1IBc6BpBsAfKZM zJGPzzL3bhZtF2dXg/8X650IqEbkGCq6Gus5j1HEW2AiGpqUtnQXnCiCHvy1Y2+K 4BZZB4cwz3rOqfcWRXZtM6+9OulXbwvPC3Z8VcByOEEcQyIOGS5IMltMcw857NlQ 2ppmL3ZaXvSieVrIItldfskFNO5jyYG3jEgNlfl9JMyjVGOZCmo= =rRKd -----END PGP SIGNATURE----- --swunxSV8odEKHzY1--