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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 1F7D3C433DB for ; Thu, 21 Jan 2021 20:56:50 +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 9D2FD205CB for ; Thu, 21 Jan 2021 20:56:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9D2FD205CB 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]:33262 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l2h0a-0002T5-FZ for qemu-devel@archiver.kernel.org; Thu, 21 Jan 2021 15:56:48 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:52454) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l2gzN-0001lU-Si for qemu-devel@nongnu.org; Thu, 21 Jan 2021 15:55:35 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:38590) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l2gzH-0003CT-G7 for qemu-devel@nongnu.org; Thu, 21 Jan 2021 15:55:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611262526; 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=ouuINGgZVUfNRHgze7BWNbcQFVs0Yf7zkGyglpslQSI=; b=aCfo6HHVumfQpYvCFeOPLctGh9s4y3J4GTd3iVsrUBl3hiqkX2KREPrK3MuMdq+KdursHa iJn0y/fzrxPSm0SHAyw+DMhS4ma0e4x0u2QxtlZXg/HTpQYoiQ4BgDDpCCiy2MGvwAziOF SBM8ErkWJlRyiCjtFFrK2AvaJiAIuOA= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-184-3L_P_ZHaMuSDB9enTlKLfw-1; Thu, 21 Jan 2021 15:55:23 -0500 X-MC-Unique: 3L_P_ZHaMuSDB9enTlKLfw-1 Received: by mail-wr1-f71.google.com with SMTP id x12so1833726wrw.21 for ; Thu, 21 Jan 2021 12:55:23 -0800 (PST) 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:reply-to :from:date:message-id:subject:to:cc:content-transfer-encoding; bh=ouuINGgZVUfNRHgze7BWNbcQFVs0Yf7zkGyglpslQSI=; b=WcPkh1N+GMU7DDJTQUISFxsWtRn+/IF2OFQ2FepZB4HgzrWc9RzsY4QfsnJ3+ToyWJ MgCH6gOB2bAl7TIz+2uwq58ZM5n9Y5++4DYdoUCDUliSTkNSKbNmc9jH7k+ZKI0pQxgS tk3m5RnFuwlhKEeMMNV+BC5js78J2a7rn51bfO97LZGg+XlSw4KlX0dO7/fGB0B34VmC ZaVaRhggYuMNKuWKWHGEe2LNcQ6wQS9mbRTFBohUbHiFLWq8aI/WDoly29O9Yyyv1gP1 UUgMDoXEorKpDnXl4dwVU5wLOwRf0SFeVQ+t8h5gwlQrFDhNcL+jhzibPOJewbWvMgpI uNYQ== X-Gm-Message-State: AOAM532zofBzzXV2JzdrdtW/U2bTF/+otgc3+1mxluSntQM5yLiGUUvk i2aOjDV3vBRIstMa/rE6SN0BVRwxkL/cuABsOHdyvR0S8GtkdbZIY9CYC9OpQuritd0UAN84Oki ZniNyCJyM+3bJWDTeluD70UpxbuEggXE= X-Received: by 2002:adf:e541:: with SMTP id z1mr1219088wrm.143.1611262522255; Thu, 21 Jan 2021 12:55:22 -0800 (PST) X-Google-Smtp-Source: ABdhPJzrU54K7gimpyH5U9KTkU3aFAghlRz5rCiIfMKNh+Xf1rph5IImkn/K24nMRr7+YYO1/+8eCtJu2L6Pudqx09g= X-Received: by 2002:adf:e541:: with SMTP id z1mr1219068wrm.143.1611262521927; Thu, 21 Jan 2021 12:55:21 -0800 (PST) MIME-Version: 1.0 References: <0A9D3682-CE03-4984-AC06-83DA0ABF7BDF@kamp.de> In-Reply-To: From: Jason Dillaman Date: Thu, 21 Jan 2021 15:55:10 -0500 Message-ID: Subject: Re: [PATCH 7/7] block/rbd: change request alignment to 1 byte To: Peter Lieven Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jdillama@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=63.128.21.124; envelope-from=jdillama@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.168, 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=unavailable 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: , Reply-To: dillaman@redhat.com Cc: Kevin Wolf , Christian Theune , qemu-devel , qemu-block , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jan 21, 2021 at 3:29 PM Peter Lieven wrote: > > Am 21.01.21 um 20:42 schrieb Jason Dillaman: > > On Wed, Jan 20, 2021 at 6:01 PM Peter Lieven wrote: > >> > >>> Am 19.01.2021 um 15:20 schrieb Jason Dillaman : > >>> > >>> =EF=BB=BFOn Tue, Jan 19, 2021 at 4:36 AM Peter Lieven wr= ote: > >>>>> Am 18.01.21 um 23:33 schrieb Jason Dillaman: > >>>>> On Fri, Jan 15, 2021 at 10:39 AM Peter Lieven wrote: > >>>>>> Am 15.01.21 um 16:27 schrieb Jason Dillaman: > >>>>>>> On Thu, Jan 14, 2021 at 2:59 PM Peter Lieven wrote: > >>>>>>>> Am 14.01.21 um 20:19 schrieb Jason Dillaman: > >>>>>>>>> On Sun, Dec 27, 2020 at 11:42 AM Peter Lieven wrot= e: > >>>>>>>>>> since we implement byte interfaces and librbd supports aio on = byte granularity we can lift > >>>>>>>>>> the 512 byte alignment. > >>>>>>>>>> Signed-off-by: Peter Lieven > >>>>>>>>>> --- > >>>>>>>>>> block/rbd.c | 2 -- > >>>>>>>>>> 1 file changed, 2 deletions(-) > >>>>>>>>>> diff --git a/block/rbd.c b/block/rbd.c > >>>>>>>>>> index 27b4404adf..8673e8f553 100644 > >>>>>>>>>> --- a/block/rbd.c > >>>>>>>>>> +++ b/block/rbd.c > >>>>>>>>>> @@ -223,8 +223,6 @@ done: > >>>>>>>>>> static void qemu_rbd_refresh_limits(BlockDriverState *bs, Erro= r **errp) > >>>>>>>>>> { > >>>>>>>>>> BDRVRBDState *s =3D bs->opaque; > >>>>>>>>>> - /* XXX Does RBD support AIO on less than 512-byte alignme= nt? */ > >>>>>>>>>> - bs->bl.request_alignment =3D 512; > >>>>>>>>> Just a suggestion, but perhaps improve discard alignment, max d= iscard, > >>>>>>>>> optimal alignment (if that's something QEMU handles internally)= if not > >>>>>>>>> overridden by the user. > >>>>>>>> Qemu supports max_discard and discard_alignment. Is there a call= to get these limits > >>>>>>>> from librbd? > >>>>>>>> What do you mean by optimal_alignment? The object size? > >>>>>>> krbd does a good job of initializing defaults [1] where optimal a= nd > >>>>>>> discard alignment is 64KiB (can actually be 4KiB now), max IO siz= e for > >>>>>>> writes, discards, and write-zeroes is the object size * the strip= e > >>>>>>> count. > >>>>>> Okay, I will have a look at it. If qemu issues a write, discard, w= rite_zero greater than > >>>>>> obj_size * stripe count will librbd split it internally or will t= he request fail? > >>>>> librbd will handle it as needed. My goal is really just to get the > >>>>> hints down the guest OS. > >>>>>> Regarding the alignment it seems that rbd_dev->opts->alloc_size is= something that comes from the device > >>>>>> configuration and not from rbd? I don't have that information insi= de the Qemu RBD driver. > >>>>> librbd doesn't really have the information either. The 64KiB guess > >>>>> that krbd uses was a compromise since that was the default OSD > >>>>> allocation size for HDDs since Luminous. Starting with Pacific that > >>>>> default is going down to 4KiB. > >>>> I will try to adjust these values as far as it is possible and makes= sense. > >>>> Is there a way to check the minimum supported OSD release in the bac= kend from librbd / librados? > >>> It's not a minimum -- RADOS will gladly access 1 byte writes as well. > >>> It's really just the optimal (performance and space-wise). Sadly, > >>> there is no realistic way to query this data from the backend. > >> So you would suggest to advertise an optimal transfer length of 64k an= d max transfer length of obj size * stripe count to the guest unless we hav= e an API in the future to query these limits from the backend? > > I'll open a Ceph tracker ticket to expose these via the API in a future= release. > > > That would be good to have! > > > > > >> I would leave request alignment at 1 byte as otherwise Qemu will issue= RMWs for all write requests that do not align. Everything that comes from = a guest OS is very likely 4k aligned anyway. > > My goal is definitely not to have QEMU do any extra work for splitting > > or aligning IOs. I am really only trying to get hints passed down the > > guest via the virtio drivers. If there isn't the plumbing in QEMU for > > that yet, disregard. > > > From what I read from the code Qemu emulates the Block Limits VPD Page fo= r virtio-scsi, but the limits there are not taken from the backend driver. = They can be passed as config to the virtio-scsi device. > > However, Qemu uses all the Block Limit that can be found in include/block= /block_int.h in the BlockLimits struct to generate optimal requests if it c= omes to block operations like mirroring, or zeroing of a whole > > device etc. Some of the alignments (e.g. the request alignment) have dire= ct influence and make Qemu split requests from the guest or even make RMW c= ycles. > > If my understanding is incorrect please anyone correct me. > > > It would indeed be nice to have an option to propagate the settings from = the backend driver into the Guest. But from my understanding this is not th= ere yet. > > > So I would leave it as it. Drop the request_alignment =3D 512 (like in th= e patch) and just advertise the cluster_size at obj_size. This is already i= n the rbd driver today. > > The cluster_size e.g. is used in any qemu-img convert operation to align = read / write requests and size them apropiately. +1 to leave as-is until we can pass those hints down. > Peter > > Thanks! --=20 Jason