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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 05D90C3A59F for ; Mon, 26 Aug 2019 13:48:48 +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 D4B95217F5 for ; Mon, 26 Aug 2019 13:48:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D4B95217F5 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]:53004 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i2FMU-0006Um-Qb for qemu-devel@archiver.kernel.org; Mon, 26 Aug 2019 09:48:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37179) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i2FKG-0005vv-3K for qemu-devel@nongnu.org; Mon, 26 Aug 2019 09:46:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i2FKF-0003Do-2Z for qemu-devel@nongnu.org; Mon, 26 Aug 2019 09:46:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43060) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i2FKC-0003As-9n; Mon, 26 Aug 2019 09:46:24 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 030263082B43; Mon, 26 Aug 2019 13:46:23 +0000 (UTC) Received: from [10.3.116.234] (ovpn-116-234.phx2.redhat.com [10.3.116.234]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4943B5D9CD; Mon, 26 Aug 2019 13:46:22 +0000 (UTC) To: Nir Soffer , qemu-devel@nongnu.org References: <20190825220329.7942-1-nsoffer@redhat.com> <20190825220329.7942-2-nsoffer@redhat.com> From: Eric Blake Openpgp: preference=signencrypt Autocrypt: addr=eblake@redhat.com; keydata= xsBNBEvHyWwBCACw7DwsQIh0kAbUXyqhfiKAKOTVu6OiMGffw2w90Ggrp4bdVKmCaEXlrVLU xphBM8mb+wsFkU+pq9YR621WXo9REYVIl0FxKeQo9dyQBZ/XvmUMka4NOmHtFg74nvkpJFCD TUNzmqfcjdKhfFV0d7P/ixKQeZr2WP1xMcjmAQY5YvQ2lUoHP43m8TtpB1LkjyYBCodd+LkV GmCx2Bop1LSblbvbrOm2bKpZdBPjncRNob73eTpIXEutvEaHH72LzpzksfcKM+M18cyRH+nP sAd98xIbVjm3Jm4k4d5oQyE2HwOur+trk2EcxTgdp17QapuWPwMfhaNq3runaX7x34zhABEB AAHNHkVyaWMgQmxha2UgPGVibGFrZUByZWRoYXQuY29tPsLAegQTAQgAJAIbAwULCQgHAwUV CgkICwUWAgMBAAIeAQIXgAUCS8fL9QIZAQAKCRCnoWtKJSdDahBHCACbl/5FGkUqJ89GAjeX RjpAeJtdKhujir0iS4CMSIng7fCiGZ0fNJCpL5RpViSo03Q7l37ss+No+dJI8KtAp6ID+PMz wTJe5Egtv/KGUKSDvOLYJ9WIIbftEObekP+GBpWP2+KbpADsc7EsNd70sYxExD3liwVJYqLc Rw7so1PEIFp+Ni9A1DrBR5NaJBnno2PHzHPTS9nmZVYm/4I32qkLXOcdX0XElO8VPDoVobG6 gELf4v/vIImdmxLh/w5WctUpBhWWIfQDvSOW2VZDOihm7pzhQodr3QP/GDLfpK6wI7exeu3P pfPtqwa06s1pae3ad13mZGzkBdNKs1HEm8x6zsBNBEvHyWwBCADGkMFzFjmmyqAEn5D+Mt4P zPdO8NatsDw8Qit3Rmzu+kUygxyYbz52ZO40WUu7EgQ5kDTOeRPnTOd7awWDQcl1gGBXgrkR pAlQ0l0ReO57Q0eglFydLMi5bkwYhfY+TwDPMh3aOP5qBXkm4qIYSsxb8A+i00P72AqFb9Q7 3weG/flxSPApLYQE5qWGSXjOkXJv42NGS6o6gd4RmD6Ap5e8ACo1lSMPfTpGzXlt4aRkBfvb NCfNsQikLZzFYDLbQgKBA33BDeV6vNJ9Cj0SgEGOkYyed4I6AbU0kIy1hHAm1r6+sAnEdIKj cHi3xWH/UPrZW5flM8Kqo14OTDkI9EtlABEBAAHCwF8EGAEIAAkFAkvHyWwCGwwACgkQp6Fr SiUnQ2q03wgAmRFGDeXzc58NX0NrDijUu0zx3Lns/qZ9VrkSWbNZBFjpWKaeL1fdVeE4TDGm I5mRRIsStjQzc2R9b+2VBUhlAqY1nAiBDv0Qnt+9cLiuEICeUwlyl42YdwpmY0ELcy5+u6wz mK/jxrYOpzXKDwLq5k4X+hmGuSNWWAN3gHiJqmJZPkhFPUIozZUCeEc76pS/IUN72NfprZmF Dp6/QDjDFtfS39bHSWXKVZUbqaMPqlj/z6Ugk027/3GUjHHr8WkeL1ezWepYDY7WSoXwfoAL 2UXYsMAr/uUncSKlfjvArhsej0S4zbqim2ZY6S8aRWw94J3bSvJR+Nwbs34GPTD4Pg== Organization: Red Hat, Inc. Message-ID: <65085dba-f180-8a4e-8464-65e91323b69b@redhat.com> Date: Mon, 26 Aug 2019 08:46:21 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190825220329.7942-2-nsoffer@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="YTj0oZNE5HcNsOPilnzzqWriS3UfpewsV" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Mon, 26 Aug 2019 13:46:23 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 1/2] block: posix: Always allocate the first block 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: Kevin Wolf , Nir Soffer , qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --YTj0oZNE5HcNsOPilnzzqWriS3UfpewsV Content-Type: multipart/mixed; boundary="i4l5PyZtRVjhkhQCMB3570w2ZChm5Ki5B"; protected-headers="v1" From: Eric Blake To: Nir Soffer , qemu-devel@nongnu.org Cc: Kevin Wolf , Nir Soffer , qemu-block@nongnu.org, Max Reitz Message-ID: <65085dba-f180-8a4e-8464-65e91323b69b@redhat.com> Subject: Re: [Qemu-devel] [PATCH v2 1/2] block: posix: Always allocate the first block References: <20190825220329.7942-1-nsoffer@redhat.com> <20190825220329.7942-2-nsoffer@redhat.com> In-Reply-To: <20190825220329.7942-2-nsoffer@redhat.com> --i4l5PyZtRVjhkhQCMB3570w2ZChm5Ki5B Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 8/25/19 5:03 PM, Nir Soffer wrote: > When creating an image with preallocation "off" or "falloc", the first > block of the image is typically not allocated. When using Gluster > storage backed by XFS filesystem, reading this block using direct I/O > succeeds regardless of request length, fooling alignment detection. >=20 > In this case we fallback to a safe value (4096) instead of the optimal > value (512), which may lead to unneeded data copying when aligning > requests. Allocating the first block avoids the fallback. >=20 > Here is a table comparing the total time spent: >=20 > Type Before(s) After(s) Diff(%) > --------------------------------------- > real 530.028 469.123 -11.4 > user 17.204 10.768 -37.4 > sys 17.881 7.011 -60.7 >=20 > We can see very clear improvement in CPU usage. Nice justification. > +/* > + * Help alignment probing by allocating the first block. > + * > + do { > + n =3D pwrite(fd, buf, write_size, 0); > + } while (n =3D=3D -1 && errno =3D=3D EINTR); > + > + qemu_vfree(buf); qemu_vfree() can corrupt errno... > + > + return (n =3D=3D -1) ? -errno : 0; =2E..which means you may be returning an unexpected value here. Either we should patch qemu_vfree() to guarantee that errno is preserved, or you locally capture errno before calling it here. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --i4l5PyZtRVjhkhQCMB3570w2ZChm5Ki5B-- --YTj0oZNE5HcNsOPilnzzqWriS3UfpewsV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAl1j4q0ACgkQp6FrSiUn Q2rlAQgAmVqFA4jZNywuLmrqI6OwWfZ4jPYy0bELI7c46qisseXwFMAlyrrpP8vd 4S/uyWDG5RWFyjXfaC4otN9IFn2rrvKwnu11Jx7N7IvTnURYlK5sfWbsXzoX49+L fVvAAdkEJtzsGyJ1tdgRApqTQKFu/jcwptWRHWvqb8bHVIOs5q3q2S9gp0Mprtw/ njGWyAu5ArEoAdiVeasrKkGLSe+ZM8DJ/vMqh5fQn4m0Ku/u7AF7sdQOVpKclEsl DHrtMy+o8GYbwQysp0qfiuvtSAr53qqJU3Y0Um6RDHm0Xjs9Su/WTATXfkb26x/y lETweizTKPrpxnckIrlnfAnRq6czyQ== =IGU/ -----END PGP SIGNATURE----- --YTj0oZNE5HcNsOPilnzzqWriS3UfpewsV--