From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from xc.sipsolutions.net ([83.246.72.84]:42633 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761526AbYEHXU3 (ORCPT ); Thu, 8 May 2008 19:20:29 -0400 Subject: Re: iwlwifi and tx info in skb->cb From: Johannes Berg To: Tomas Winkler Cc: Ron Rindjunsky , linux-wireless In-Reply-To: <1210288662.3547.85.camel@johannes.berg> (sfid-20080509_011655_234582_DBEBB846) References: <1210197711.3547.1.camel@johannes.berg> <1ba2fa240805071629i6c7336f6y61a7c9690820ef5e@mail.gmail.com> <1210203054.3547.12.camel@johannes.berg> <1ba2fa240805071721i3d1e3258s1e8c024c4cae9239@mail.gmail.com> <1210255522.3547.48.camel@johannes.berg> <1ba2fa240805081507j7cf991ffo5bae443b0b77a39e@mail.gmail.com> <1210284656.3547.76.camel@johannes.berg> <1ba2fa240805081528t45d7810cjfd553bf99daff096@mail.gmail.com> <1210285845.3547.81.camel@johannes.berg> <1ba2fa240805081616l3f49d770pefd517076a06b3ef@mail.gmail.com> (sfid-20080509_011511_095937_36DE1999) <1210288662.3547.85.camel@johannes.berg> (sfid-20080509_011655_234582_DBEBB846) Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-MJptV3DtjRSVXN2U83bU" Date: Fri, 09 May 2008 01:20:15 +0200 Message-Id: <1210288815.3547.88.camel@johannes.berg> (sfid-20080509_011926_539761_F07ADB9D) Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: --=-MJptV3DtjRSVXN2U83bU Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Fri, 2008-05-09 at 01:17 +0200, Johannes Berg wrote: > > > That's not really related to wireless at all, if you want to do > > > zero-copy IO then you need to checksum when the stuff hits the wire > > > which means out of hardware buffers, which some hardware (including > > > 802.11) doesn't support so you need to copy, nothing wireless specif= ic > > > here :) > > > > >=20 > > The FCS/CRS checksum of the wireless packet is performed in the HW but > > why should I care about IP layer? >=20 > Because the data you're sending is sent via TCP? Basically, it boils down to this: If you want to checksum the data in software then you need to checksum a snapshot of the data and not allow the application to modify it after you have checksummed it, so you need to make a copy and then checksum it after copying. But if you're making a copy anyway, you can put it all into one buffer too. johannes --=-MJptV3DtjRSVXN2U83bU Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Comment: Johannes Berg (powerbook) iQIVAwUASCOKrqVg1VMiehFYAQLOSA//X5FsODZFmBhq5MbyV6Yo0O2OlQ9GbjnX petlEbnmC31wOQ8jDCSHAk9I9wtNKXOS97n+BKk0Ev/0MBJq4X6gKz4MWru4uUYW xV9fAiHWYeA0NXNXt6F9he94yM3dgrN6h4Z7xRh8So5M6zAf41bWPMCT/q/FS/Eh kSyNkxrrAvvPrYFGJaO0bqZ74wyNzUP2vMfEJEyy+t2M7xsjhsB2ulHpIdl5R22e ZvRn6IrMAj9Dtg/as9LzoHpGt58hBAdndB+TVSM2GcRkpm8gk5vzI5a0dAs/9Xtl t4r0xw4FOWVauDo8jujOGhOkKhbBQFGTNJWVw7P3nod9jOadMSsOWlsiu+GWcSCj ukwG2lHTbQiett9o9sEBcc8rp/H+hF0f/HEsUyVZoqlKImit8cxACg36l6jlxBKN KglOBk6qb2CT6VKX44VyBQcMR4pdFDoUZ6NRWZpDudM9rgQCTrzvrk0oxmSUehts 2JWpwkMr5eQCSViCrlLEclBxQUkoDZIg7lcdF/RFQWrSJ3m21Who942QQ9h5pZZ3 Z2a/FxeH0reCOAz8sPApzZM7TwBpJ4VaYTffVNBYa+drGO9R0KtphOzn3MgVsCuI zEJ2mdNDwp/vPEjqvFhwLNGvz66aeBKOfAtw72AvCGRUXicHqFbI59xUudxd050N YVYLWfEF830= =Iwir -----END PGP SIGNATURE----- --=-MJptV3DtjRSVXN2U83bU--