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=-4.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 A563AC4338F for ; Sun, 22 Aug 2021 12:11:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E3046128A for ; Sun, 22 Aug 2021 12:11:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231468AbhHVMMP (ORCPT ); Sun, 22 Aug 2021 08:12:15 -0400 Received: from mail.kernel.org ([198.145.29.99]:51860 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229961AbhHVMML (ORCPT ); Sun, 22 Aug 2021 08:12:11 -0400 Received: by mail.kernel.org (Postfix) with ESMTPS id 63ECC61354 for ; Sun, 22 Aug 2021 12:11:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1629634290; bh=/UsrHwTZxwhF1qFbCYtV6D1yNL4w88tq4OpRQLqioHs=; h=From:To:Subject:Date:In-Reply-To:References:From; b=BH/qzpeY0KWJLuH+Hi29rAsL7WNzg/BoiT2jtMxb5+w2nkV/MAx/IFQGxzqcXlYDF aKHJP+9kIfaG3ebXJymRtJUeLedGiTyqPEKxA10cdIxoqiNRZzZcOFt8osFhYGIRlC A/BrKomhhMoOfP/p83a792SVkH8Tau2MdNSaNybja+HOl4Vp7yc1+nJm8bCqj8+U/c me5OxoVorzipx66fi17S6CxpkFQF3lFlWHeBW9U+Q/nJAvzAMaRu7p1QTvfjHHZ4pl Ub6Q3XSJ9eLxG0UkLNyp+iY62YdRuK/M5tW3O+iU77vph2AIDBC4eAk+glda++PHai Y2eg2kS4apArw== From: bugzilla-daemon@bugzilla.kernel.org To: kvm@vger.kernel.org Subject: [Bug 199727] CPU freezes in KVM guests during high IO load on host Date: Sun, 22 Aug 2021 12:11:30 +0000 X-Bugzilla-Reason: None X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: AssignedTo virtualization_kvm@kernel-bugs.osdl.org X-Bugzilla-Product: Virtualization X-Bugzilla-Component: kvm X-Bugzilla-Version: unspecified X-Bugzilla-Keywords: X-Bugzilla-Severity: high X-Bugzilla-Who: devzero@web.de X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P1 X-Bugzilla-Assigned-To: virtualization_kvm@kernel-bugs.osdl.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugzilla.kernel.org/ Auto-Submitted: auto-generated MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org https://bugzilla.kernel.org/show_bug.cgi?id=3D199727 --- Comment #4 from Roland Kletzing (devzero@web.de) --- http://blog.vmsplice.net/2015/08/asynchronous-file-io-on-linux-plus-ca.html "However, the io_submit(2) system call remains a treacherous ally in the qu= est for asynchronous file I/O. I don't think much has changed since 2009 in mak= ing Linux AIO the best asynchronous file I/O mechanism. The main problem is that io_submit(2) waits for I/O in some cases. It can block! This defeats the purpose of asynchronous file I/O because the caller= is stuck until the system call completes. If called from a program's event loo= p, the program becomes unresponsive until the system call returns. But even if io_submit(2) is invoked from a dedicated thread where blocking doesn't matt= er, latency is introduced to any further I/O requests submitted in the same io_submit(2) call. Sources of blocking in io_submit(2) depend on the file system and block dev= ices being used. There are many different cases but in general they occur because file I/O code paths contain synchronous I/O (for metadata I/O or page cache write-out) as well as locks/waiting (for serializing operations). This is w= hy the io_submit(2) system call can be held up while submitting a request. This means io_submit(2) works best on fully-allocated files, volumes, or bl= ock devices. Anything else is likely to result in blocking behavior and cause p= oor performance." --=20 You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.=