From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5E553182 for ; Sun, 9 Mar 2025 00:06:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741478776; cv=none; b=ErX3L1rCcj5LPlXqBdSPGbyEfjkANPRH3pLyVGtnEw0KaUnZUpiGk/SZ1aPocO5fAPI7Wf3idbjF0Jmp+z9J9gjVlH/k28UKjmNoJem13jzaO7tKr6qppOkR0Of1rf9MMUuvX/YxxTN2QRtoWB+/SqD9qNguzH/Wza7VGMmc2qg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741478776; c=relaxed/simple; bh=IsJdLezirQBjniJmTCKLyMuVKEgaZpOifJ53Nl8gEjM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Z9pehO+QFQNhinIq+BzkAh1pDMoEuy3fVKCbsG3tvg6e5dmTZw0PTkytvlSAR7+I5q8xjjxbTbNUjg/Q5EZNPxUvxcPmBY7nAGVSQkUX9qmggX//qzQh84Xwb/eaLy8rYU3LJFnmi2z59TouiJIpuH1tIBMdCERxeVcy0HamP3s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=fN1giR58; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fN1giR58" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741478773; 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=2V7bQ4VK6TsBeGHH+0dQ7PDHfL43pm6Etkd1tSAFig4=; b=fN1giR58KDjUV4NvoLsBaxJ1C8B6KHQe+6IuuSdT/VcVdTKSxmG9I+Z+IpJEorflJEA5Zv 9FBhgFR1LJUWKk+nx3GEroYwXMZO25AFZQKlLSYeV6X8hlV2l8/deoyX9tdc63nwOVagC9 qE8XZMEsAWQ/r7Dt2ex8yDyvqj3M04c= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-231-8VWtHirSMn68_xXxg8d3KA-1; Sat, 08 Mar 2025 19:06:10 -0500 X-MC-Unique: 8VWtHirSMn68_xXxg8d3KA-1 X-Mimecast-MFC-AGG-ID: 8VWtHirSMn68_xXxg8d3KA_1741478768 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6EACD1956087; Sun, 9 Mar 2025 00:06:08 +0000 (UTC) Received: from fedora (unknown [10.72.120.5]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8D1E7180AF7A; Sun, 9 Mar 2025 00:05:58 +0000 (UTC) Date: Sun, 9 Mar 2025 08:05:52 +0800 From: Ming Lei To: Mikulas Patocka Cc: Dave Chinner , Christoph Hellwig , Jens Axboe , Jooyung Han , Alasdair Kergon , Mike Snitzer , Heinz Mauelshagen , zkabelac@redhat.com, dm-devel@lists.linux.dev, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] the dm-loop target Message-ID: References: <7d6ae2c9-df8e-50d0-7ad6-b787cb3cfab4@redhat.com> <8adb8df2-0c75-592d-bc3e-5609bb8de8d8@redhat.com> <1fde6ab6-bfba-3dc4-d7fb-67074036deb0@redhat.com> <81b037c8-8fea-2d4c-0baf-d9aa18835063@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <81b037c8-8fea-2d4c-0baf-d9aa18835063@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On Fri, Mar 07, 2025 at 04:21:58PM +0100, Mikulas Patocka wrote: > > I didn't say you were. I said the concept that dm-loop is based on > > is fundamentally flawed and that your benchmark setup does not > > reflect real world usage of loop devices. > > > Where are the bug reports about the loop device being slow and the > > analysis that indicates that it is unfixable? > > So, I did benchmarks on an enterprise nvme drive (SAMSUNG > MZPLJ1T6HBJR-00007). I stacked ext4/loop/ext4, xfs/loop/xfs (using losetup > --direct-io=on), ext4/dm-loop/ext4 and xfs/dm-loop/xfs. And loop is slow. > > synchronous I/O: > fio --direct=1 --bs=4k --runtime=10 --time_based --numjobs=12 --ioengine=psync --iodepth=1 --group_reporting=1 --filename=/mnt/test2/l -name=job --rw=rw > raw block device: > READ: bw=399MiB/s (418MB/s), 399MiB/s-399MiB/s (418MB/s-418MB/s), io=3985MiB (4179MB), run=10001-10001msec > WRITE: bw=399MiB/s (418MB/s), 399MiB/s-399MiB/s (418MB/s-418MB/s), io=3990MiB (4184MB), run=10001-10001msec > ext4/loop/ext4: > READ: bw=223MiB/s (234MB/s), 223MiB/s-223MiB/s (234MB/s-234MB/s), io=2232MiB (2341MB), run=10002-10002msec > WRITE: bw=223MiB/s (234MB/s), 223MiB/s-223MiB/s (234MB/s-234MB/s), io=2231MiB (2339MB), run=10002-10002msec > xfs/loop/xfs: > READ: bw=220MiB/s (230MB/s), 220MiB/s-220MiB/s (230MB/s-230MB/s), io=2196MiB (2303MB), run=10001-10001msec > WRITE: bw=219MiB/s (230MB/s), 219MiB/s-219MiB/s (230MB/s-230MB/s), io=2193MiB (2300MB), run=10001-10001msec > ext4/dm-loop/ext4: > READ: bw=338MiB/s (355MB/s), 338MiB/s-338MiB/s (355MB/s-355MB/s), io=3383MiB (3547MB), run=10002-10002msec > WRITE: bw=338MiB/s (355MB/s), 338MiB/s-338MiB/s (355MB/s-355MB/s), io=3385MiB (3549MB), run=10002-10002msec > xfs/dm-loop/xfs: > READ: bw=375MiB/s (393MB/s), 375MiB/s-375MiB/s (393MB/s-393MB/s), io=3752MiB (3934MB), run=10002-10002msec > WRITE: bw=376MiB/s (394MB/s), 376MiB/s-376MiB/s (394MB/s-394MB/s), io=3756MiB (3938MB), run=10002-10002msec > > asynchronous I/O: > fio --direct=1 --bs=4k --runtime=10 --time_based --numjobs=12 --ioengine=libaio --iodepth=16 --group_reporting=1 --filename=/mnt/test2/l -name=job --rw=rw > raw block device: > READ: bw=1246MiB/s (1306MB/s), 1246MiB/s-1246MiB/s (1306MB/s-1306MB/s), io=12.2GiB (13.1GB), run=10001-10001msec > WRITE: bw=1247MiB/s (1308MB/s), 1247MiB/s-1247MiB/s (1308MB/s-1308MB/s), io=12.2GiB (13.1GB), run=10001-10001msec > ext4/loop/ext4: > READ: bw=274MiB/s (288MB/s), 274MiB/s-274MiB/s (288MB/s-288MB/s), io=2743MiB (2877MB), run=10001-10001msec > WRITE: bw=275MiB/s (288MB/s), 275MiB/s-275MiB/s (288MB/s-288MB/s), io=2747MiB (2880MB), run=10001-10001msec > xfs/loop/xfs: > READ: bw=276MiB/s (289MB/s), 276MiB/s-276MiB/s (289MB/s-289MB/s), io=2761MiB (2896MB), run=10002-10002msec > WRITE: bw=276MiB/s (290MB/s), 276MiB/s-276MiB/s (290MB/s-290MB/s), io=2765MiB (2899MB), run=10002-10002msec > ext4/dm-loop/ext4: > READ: bw=1189MiB/s (1247MB/s), 1189MiB/s-1189MiB/s (1247MB/s-1247MB/s), io=11.6GiB (12.5GB), run=10002-10002msec > WRITE: bw=1190MiB/s (1248MB/s), 1190MiB/s-1190MiB/s (1248MB/s-1248MB/s), io=11.6GiB (12.5GB), run=10002-10002msec > xfs/dm-loop/xfs: > READ: bw=1209MiB/s (1268MB/s), 1209MiB/s-1209MiB/s (1268MB/s-1268MB/s), io=11.8GiB (12.7GB), run=10001-10001msec > WRITE: bw=1210MiB/s (1269MB/s), 1210MiB/s-1210MiB/s (1269MB/s-1269MB/s), io=11.8GiB (12.7GB), run=10001-10001msec Hi Mikulas, Please try the following patchset: https://lore.kernel.org/linux-block/20250308162312.1640828-1-ming.lei@redhat.com/ which tries to handle IO in current context directly via NOWAIT, and supports MQ for loop since 12 io jobs are applied in your test. With this change, I can observe similar perf data on raw block device and loop/xfs over mq-virtio-scsi & nvme in my test VM. 1) try single queue first by `modprobe loop` 2) then try MQ by 'modprobe loop nr_hw_queues=4' If it still doesn't work, please provide fio log for both `raw block device` and 'loop/xfs', which may provide some clue for the big perf gap. Thanks, Ming