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=202502 header.b=OwAKuK5F; dkim-atps=neutral Received: from mail.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by passt.top (Postfix) with ESMTPS id B5B165A0638 for ; Fri, 14 Feb 2025 00:41:14 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202502; t=1739490062; bh=ETf3nHpkOc+PPPk+WAmzLukGcEJ6Pm/VT1/K8Fqa3Fk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OwAKuK5FA63yxSpEF8Lvbll1kDMWUYuWxKGgJTB9W6i9/Z8K0tDQKEXdXHjn337g0 BxXKGtraVdmYKiUqepPwhxIqRyG+PAflAvcXfntr0LPUuSWMyPj0GnHPjjF44J7BED scomDIK8/3dFcT953ntnJttavzUr5NzIqZ+rJd7PfLPpBxmGYQpn8N2+gRAs30jbWY j8ejGRoEL6I62myehvb2yumN4vfiFRzxr4QrSw+lT6+OIhdypkMCYKASfHM+sezYFm wX5GXzzsxek04jqFdouwEG0z6bWsU2/YOwXqlZQXkupD8jjeDjmYlV1mOpC2IFUa2a oCoJ0EqfGroYw== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4YvBWy0d0wz4x0t; Fri, 14 Feb 2025 10:41:02 +1100 (AEDT) Date: Fri, 14 Feb 2025 10:02:56 +1100 From: David Gibson To: Stefano Brivio Subject: Re: [PATCH] tcp, tcp_splice: Don't set SO_SNDBUF and SO_RCVBUF to maximum values Message-ID: References: <20250213221650.4086105-1-sbrivio@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="B3g+FDtg/wFp/KoF" Content-Disposition: inline In-Reply-To: <20250213221650.4086105-1-sbrivio@redhat.com> Message-ID-Hash: 6DV3JD7N324VFL4D63NDMJ7JTHCDQCSQ X-Message-ID-Hash: 6DV3JD7N324VFL4D63NDMJ7JTHCDQCSQ 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: --B3g+FDtg/wFp/KoF Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Feb 13, 2025 at 11:16:50PM +0100, Stefano Brivio wrote: > I added this a long long time ago because it dramatically improved > throughput back then: with rmem_max and wmem_max >=3D 4 MiB, we would > force send and receive buffer sizes for TCP sockets to the maximum > allowed value. >=20 > This effectively disables TCP auto-tuning, which would otherwise allow > us to exceed those limits, as crazy as it might sound. But in any > case, it made sense. >=20 > Now that we have zero (internal) copies on every path, plus vhost-user > support, it turns out that these settings are entirely obsolete. I get > substantially the same throughput in every test we perform, even with > very short durations (one second). >=20 > The settings are not just useless: they actually cause us quite some > trouble on guest state migration, because they lead to huge queues > that need to be moved as well. >=20 > Drop those settings. >=20 > Signed-off-by: Stefano Brivio Hooray! Reviewed-by: David Gibson --=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 --B3g+FDtg/wFp/KoF Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmeueh8ACgkQzQJF27ox 2Ge8JA/+I8UbkYGT3nYiR2h4+7DWEE/8s7+uNxpDS52RUe5yl2x7MIvYvtztJiSG CW9QDqPJ5gAljY4lr07WKAIIVBerSmx+0Wr8z6zypThRtk0oyZjCL482fLoTiQ+c umi94WjiaRp+VZgTp8+VEHs/760Y1XUfWBCw4mX4ooaSWBe2Y8ahVlBIDzezplM7 a5cL+EoMBfuC11RpHPiUItJLvrp0vx+OdXiedeTqJ9VkFoZZuBANWM8YkNpas2T8 1PQh3XC8qsaa4zjiUbDXM1tC4nj1UpMZM68G0bB2cpawYPYcd9aZ5Slf6UU3P0xE dG91osEd0vz/EBucLtIB3Gc3CaOhUcXwcv3VLylzc1BPsDfEppyJIlhdBWNd4x9u 1WjdZS9f18ckGJmDNm+eCdh1Qfiz6gxi6/eD0KmaWiiNYyoDhNpXgFwLfCeLQLky DiO3Gv3V8AuI6v8UJjvpeIrtxgK/hlbBLPCC9+JZdsFsvjiWAhDs5r1mk+0Y0K9Z blMWSiMpKbGrS8gPMcvWe5ri1VLyOudJClcp2CR4cVmJWOpDRXqn/Rh44ZzOL09q iQQlaS2ipl92yIA4ytQErK5PrfOLTQk2e2cbpNRssfVP5qflGQTkApXDFrikG87p 0Bg23gfh+XucLPPJbWxj6gYGq+MEyLVAJwTZRnDkIpjVeIYITlc= =w2z/ -----END PGP SIGNATURE----- --B3g+FDtg/wFp/KoF--