From owner-freebsd-current@FreeBSD.ORG Fri Jul 27 05:52:09 2012 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id D9507106566C for ; Fri, 27 Jul 2012 05:52:09 +0000 (UTC) (envelope-from adrian.chadd@gmail.com) Received: from mail-gh0-f182.google.com (mail-gh0-f182.google.com [209.85.160.182]) by mx1.freebsd.org (Postfix) with ESMTP id 92ACE8FC08 for ; Fri, 27 Jul 2012 05:52:09 +0000 (UTC) Received: by ghbz22 with SMTP id z22so3326171ghb.13 for ; Thu, 26 Jul 2012 22:52:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=WcjbAVPK8BWvTjHlkDActlekf8kuAamU4d9QmnytGvk=; b=pZfhZ+6nd9daUnMUVGicx/VE7Fp6ZBGkSLZpkR2AFwQoJC9QPNWCQvA2H253/UzOM+ Uw/B3fxfG0DbDk2h5A3EU1KHp30WCFLyF9dP0W5zlpwvhnXsgRCNhPRxFePzcaOE7xgK H0e47JDQR019zUcpUuQaSO+do+W5DkH44VCq+qLXjSYhbnUM+NfF70f+wk3h8vlys2uU SCqZrPmJwxHbrXZKAos9Y15jLDBFFGucTPEM5/04NsMHk15g6cHSti1M+3lR+rpslR5j PJLP5p+xTy9xrWomLMBq50nZdJPYtD9DLtGJy2asv9sT3L3SgEYdPcqER0LJV90fB9RF OScQ== MIME-Version: 1.0 Received: by 10.66.74.36 with SMTP id q4mr3043487pav.13.1343368328559; Thu, 26 Jul 2012 22:52:08 -0700 (PDT) Sender: adrian.chadd@gmail.com Received: by 10.68.66.136 with HTTP; Thu, 26 Jul 2012 22:52:08 -0700 (PDT) In-Reply-To: <20120725151403.GA33640@onelab2.iet.unipi.it> References: <20120724202019.GA22927@onelab2.iet.unipi.it> <20120725151403.GA33640@onelab2.iet.unipi.it> Date: Thu, 26 Jul 2012 22:52:08 -0700 X-Google-Sender-Auth: u63peznblJ671mzSItgHkmLjrCc Message-ID: From: Adrian Chadd To: Luigi Rizzo Content-Type: text/plain; charset=ISO-8859-1 Cc: current@freebsd.org Subject: Re: RFC: use EM_LEGACY_IRQ in if_lem.c ? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 27 Jul 2012 05:52:10 -0000 On 25 July 2012 08:14, Luigi Rizzo wrote: >> I suggest doing some digging to understand why. I bet we all know the >> answer, but it would be nice to have it documented and investigated. I >> bet em(4) isn't the only device that would benefit from this? > > I am not so sure i know the answer on bare iron (and my take is that the > difference is more or less irrelevant there), but in the virtualized case > the improvement is almost surely because the code used in FAST_INTR > has a couple of MMIO accesses to disable/enable interrupts on the > card while the taskqueue runs. These are expensive in a VM > (such accesses cost ~10K cycles each, even with hw support) Hm, really? Doing these register accesses to a virtualised em NIC in a VM is that expensive, or is there something else going on I don't understand? Adrian