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=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 4F476C47096 for ; Thu, 3 Jun 2021 17:34:10 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E87BB61359 for ; Thu, 3 Jun 2021 17:34:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E87BB61359 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56196 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lorEO-0002TD-TM for qemu-devel@archiver.kernel.org; Thu, 03 Jun 2021 13:34:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60572) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lorDe-0001Ll-9S for qemu-devel@nongnu.org; Thu, 03 Jun 2021 13:33:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:49532) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lorDb-000161-Ch for qemu-devel@nongnu.org; Thu, 03 Jun 2021 13:33:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622741597; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dMM6bNhLEKxZHetUzKOGQIe41YG57f9FE1odJgEss94=; b=Aqzk9Wd6LF+GFcJFl92RmrOuyIuWr0bkb7+WhfhrTCbfeLOgITK0qC+byq7M0hKZ+6t4Rl f97hWVU1mGXNYpuixBG5FN5X3k81MoBu9pknQHLio/AaAIg6yXbBbGNS4/h+BkTPXpodqC K0dbYASnQ+PlpisUUy0czG+IoUquZY4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-601-yAXa2Z33PKORiFe_DbmsMA-1; Thu, 03 Jun 2021 13:33:14 -0400 X-MC-Unique: yAXa2Z33PKORiFe_DbmsMA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2D3518DD120; Thu, 3 Jun 2021 17:33:13 +0000 (UTC) Received: from redhat.com (ovpn-113-53.phx2.redhat.com [10.3.113.53]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ACFE75D9F2; Thu, 3 Jun 2021 17:33:12 +0000 (UTC) Date: Thu, 3 Jun 2021 12:33:11 -0500 From: Eric Blake To: Paolo Bonzini Subject: Re: [PATCH v3 3/7] block: add max_hw_transfer to BlockLimits Message-ID: <20210603173311.abker673xq6qscww@redhat.com> References: <20210603133722.218465-1-pbonzini@redhat.com> <20210603133722.218465-4-pbonzini@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210603133722.218465-4-pbonzini@redhat.com> User-Agent: NeoMutt/20210205 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.37, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jun 03, 2021 at 03:37:18PM +0200, Paolo Bonzini wrote: > For block host devices, I/O can happen through either the kernel file > descriptor I/O system calls (preadv/pwritev, io_submit, io_uring) > or the SCSI passthrough ioctl SG_IO. > > In the latter case, the size of each transfer can be limited by the > HBA, while for file descriptor I/O the kernel is able to split and > merge I/O in smaller pieces as needed. Applying the HBA limits to > file descriptor I/O results in more system calls and suboptimal > performance, so this patch splits the max_transfer limit in two: > max_transfer remains valid and is used in general, while max_hw_transfer > is limited to the maximum hardware size. max_hw_transfer can then be > included by the scsi-generic driver in the block limits page, to ensure > that the stricter hardware limit is used. > > +/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */ > +uint64_t blk_get_max_hw_transfer(BlockBackend *blk) > +{ > + BlockDriverState *bs = blk_bs(blk); > + uint64_t max = INT_MAX; This is an unaligned value; should we instead round it down to the request_alignment granularity? > + > + if (bs) { > + max = MIN_NON_ZERO(bs->bl.max_hw_transfer, bs->bl.max_transfer); > + } > + return max; > +} > + > /* Returns the maximum transfer length, in bytes; guaranteed nonzero */ > uint32_t blk_get_max_transfer(BlockBackend *blk) > { > +++ b/include/block/block_int.h > @@ -695,6 +695,13 @@ typedef struct BlockLimits { > * clamped down. */ > uint32_t max_transfer; > > + /* Maximal hardware transfer length in bytes. Applies whenever Leading /* on its own line, per our style. > + * transfers to the device bypass the kernel I/O scheduler, for > + * example with SG_IO. If larger than max_transfer or if zero, > + * blk_get_max_hw_transfer will fall back to max_transfer. > + */ Should we mandate any additional requirements on this value such as multiple of request_alignment or even power-of-2? > + uint64_t max_hw_transfer; > + > /* memory alignment, in bytes so that no bounce buffer is needed */ > size_t min_mem_alignment; > -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org