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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 1DEE8C433EF for ; Fri, 22 Apr 2022 11:51:12 +0000 (UTC) Received: from localhost ([::1]:43670 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nhrod-00045N-3l for qemu-devel@archiver.kernel.org; Fri, 22 Apr 2022 07:51:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60070) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nhqDg-0000w6-6a for qemu-devel@nongnu.org; Fri, 22 Apr 2022 06:08:56 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59023) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nhqDb-0003Sx-VL for qemu-devel@nongnu.org; Fri, 22 Apr 2022 06:08:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1650622126; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MRbwBgdxcEBnL1RNITAu3Mwkn0I4vCjaq/KWbQFgBM4=; b=InT1BZlBnaIJ2FBeqT8fPa20XglHv3VHJlyTb8HF8XHyoSEZmoZl9RA7rqs2hleybv1Byo YsBVw64bPF4XzIzOJKalIepSepqW+Oxtx3IEpUZw2XfW1tWk7L/xZB0CysDZ8OxMquiSTz 0tUtmn3wCm726Jdd0QX21z2J7fXwzBI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-466-eFCLI5lhO2eT3XxBjktNKw-1; Fri, 22 Apr 2022 06:08:43 -0400 X-MC-Unique: eFCLI5lhO2eT3XxBjktNKw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 50C07811E81; Fri, 22 Apr 2022 10:08:43 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.218]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D0E9346519B; Fri, 22 Apr 2022 10:08:41 +0000 (UTC) Date: Fri, 22 Apr 2022 11:08:39 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Fam Zheng Subject: Re: [PATCH v4] Use io_uring_register_ring_fd() to skip fd operations Message-ID: References: <20220421163648.4205-1-faithilikerun@gmail.com> <20220422083428.GA61339@fam-dell> <20220422100047.GB61339@fam-dell> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220422100047.GB61339@fam-dell> User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.9 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Damien Le Moal , Dmitry Fomichev , Stefan Hajnoczi , Sam Li , qemu-devel , Hannes Reinecke Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Apr 22, 2022 at 11:00:47AM +0100, Fam Zheng wrote: > On 2022-04-22 09:52, Daniel P. Berrangé wrote: > > On Fri, Apr 22, 2022 at 09:34:28AM +0100, Fam Zheng wrote: > > > On 2022-04-22 00:36, Sam Li wrote: > > > > Linux recently added a new io_uring(7) optimization API that QEMU > > > > doesn't take advantage of yet. The liburing library that QEMU uses > > > > has added a corresponding new API calling io_uring_register_ring_fd(). > > > > When this API is called after creating the ring, the io_uring_submit() > > > > library function passes a flag to the io_uring_enter(2) syscall > > > > allowing it to skip the ring file descriptor fdget()/fdput() > > > > operations. This saves some CPU cycles. > > > > > > > > Signed-off-by: Sam Li > > > > --- > > > > block/io_uring.c | 10 +++++++++- > > > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/block/io_uring.c b/block/io_uring.c > > > > index 782afdb433..5247fb79e2 100644 > > > > --- a/block/io_uring.c > > > > +++ b/block/io_uring.c > > > > @@ -435,8 +435,16 @@ LuringState *luring_init(Error **errp) > > > > } > > > > > > > > ioq_init(&s->io_q); > > > > - return s; > > > > + if (io_uring_register_ring_fd(&s->ring) < 0) { > > > > + /* > > > > + * Only warn about this error: we will fallback to the non-optimized > > > > + * io_uring operations. > > > > + */ > > > > + error_reportf_err(*errp, > > > > + "failed to register linux io_uring ring file descriptor"); > > > > > > IIUC errp can be NULL, so let's not dereference it without checking. So, just > > > use error_report? > > > > Plenty of people will be running kernels that lack the new feature, > > so this "failure" will be an expected scenario. We shouldn't be > > spamming the logs with any error or warning message. Assuming QEMU > > remains fully functional, merely not as optimized, we should be > > totally silent. > > Functionally, that's a very valid point. But performance wise, is it good to > have some visibility of this? Since people use io_uring instead of other > options almost certainly for performance, and here the issue does matter quite > a bit. IMHO what you describe is largely a documentation issue, and/or something for OS vendors to worry about if they want to maximise their users' performance. As long as io_uring is fully functional we shouldn't print errors on every QEMU startup, as it leads to pointless bug reports/support escalations about something that is operating normally, wasting users and vendors' time. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|