From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7A8F1C433DB for ; Mon, 25 Jan 2021 20:27:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46B89216FD for ; Mon, 25 Jan 2021 20:27:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726769AbhAYUX7 (ORCPT ); Mon, 25 Jan 2021 15:23:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732230AbhAYUXc (ORCPT ); Mon, 25 Jan 2021 15:23:32 -0500 Received: from mail-lf1-x134.google.com (mail-lf1-x134.google.com [IPv6:2a00:1450:4864:20::134]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 64845C06174A for ; Mon, 25 Jan 2021 12:22:51 -0800 (PST) Received: by mail-lf1-x134.google.com with SMTP id h7so19693369lfc.6 for ; Mon, 25 Jan 2021 12:22:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=dJpq/TlGZ0HV+h016sPhctqkjMa4DX0F273nd+8b3yc=; b=WyYUw/aSFr1MSlUVSQDIkpVX2nb/bR07JJGfFgPaPks/Rtxm58XENJ50+jWJX+AawP og0eR9vXK6kMDMpYY3OaXmhGxb+A0PlZ5HA4WnZ1Dw5gK/MvgI6MNwSZ310OOdOEOvQ4 yjtEOKXoq1epLjJRlX5bqEqCRlkkYFVFnnItU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=dJpq/TlGZ0HV+h016sPhctqkjMa4DX0F273nd+8b3yc=; b=Mj607u4Zm21ar2AukrF+rhYPtqDSCAE3w9p7xqwPUsNe3EyWouK9n/gs9/c66AlrjZ HvPFe3o9Z/BHwkFpAhNKRUTnY8IqISGNdFxW5qdVuhI9qVFzrfuOX/WH7TSPeRVDwumS M4lrWZqC2QIO0zXl5Pm5lIs2DWEikE2MiDeCFFAuYjGf+H3reUKGs21XLqVtvrWe+eIi ZMCpyptICrYT7wdboYE+Ri5c9Kv8VSIa1A2+RXJ32FBq8O0LagBav2EDESspqcxSgpUt 4PYMYUyjWjoM1WIJ8xhzZHAFIhEknd87QwflcjLsln3s2Zlq/n0iAv4riXWllWaQtwgV cssg== X-Gm-Message-State: AOAM533mG+wQeykHwMfkMEi4aS4cWmY2jZ2teMAW3KJe2AAqRhomYFXc 9864E/6zTjtmMOCO64zTZDqUgYfad7C3mInwlQJJZg== X-Google-Smtp-Source: ABdhPJxppek8k+MKygN8hDoW+cn2HFTARntbQjYbW9SLECXv7t4TbCRIWzgwjZdjZTOvP6quSKFgaVwXyprDITe+tYM= X-Received: by 2002:ac2:4f88:: with SMTP id z8mr960588lfs.141.1611606169819; Mon, 25 Jan 2021 12:22:49 -0800 (PST) MIME-Version: 1.0 References: <20210122193658.282884-1-saeed@kernel.org> <20210125195905.GA4147@nvidia.com> In-Reply-To: <20210125195905.GA4147@nvidia.com> From: Edwin Peer Date: Mon, 25 Jan 2021 12:22:13 -0800 Message-ID: Subject: Re: [pull request][net-next V10 00/14] Add mlx5 subfunction support To: Jason Gunthorpe Cc: Parav Pandit , Saeed Mahameed , "David S. Miller" , Jakub Kicinski , netdev , "linux-rdma@vger.kernel.org" , Alexander Duyck , Sridhar Samudrala , David Ahern , Kiran Patil , Jacob Keller , "Ertman, David M" , Dan Williams , Saeed Mahameed Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="000000000000498aa505b9bf4d7f" Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org --000000000000498aa505b9bf4d7f Content-Type: text/plain; charset="UTF-8" On Mon, Jan 25, 2021 at 11:59 AM Jason Gunthorpe wrote: > Every writable data mandated by the PCI spec requires very expensive > on-die SRAM to store it. That's an implementation decision. Nothing mandates that the state has to physically exist in the same structure, only that reads and writes are appropriately responded to. Parts that are read only could be generated on the fly and writes can be stored more efficiently. > We've seen Intel drivers that show their SIOV ADIs don't even have a > register file and the only PCI presence is just a write-only doorbell > page in the BAR. Right, but presumably it still needs to be at least a page. And, nothing says your device's VF BAR protocol can't be equally simple. > It is hard to argue a write-only register in a BAR page vs all the > SRIOV trappings when it comes to HW cost. Say it's double the cost? I don't know that it is, but does that warrant the additional complexity of SFs? We should try to quantify. 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