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 27510C47422 for ; Wed, 24 Jan 2024 22:02:13 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rSlIy-0000zU-IZ; Wed, 24 Jan 2024 17:01:08 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rSlIw-0000zA-In for qemu-devel@nongnu.org; Wed, 24 Jan 2024 17:01:07 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rSlIs-0005s0-0a for qemu-devel@nongnu.org; Wed, 24 Jan 2024 17:01:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1706133660; 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=SAnUBYIuiFw2VY3B2zyQtkCvm2LNngJths+XlfFPQw4=; b=cEytRFk+bazq4lPC2NaiSCc2m3leCH9OXT5RhJVPREg3J8H0T3qvkxWm8NEO48NFk4r55o Al+dn/F9LpQYWxjXn1Wftlp0I4qR+1N0pVDr5AzGxAdW9Uz+Mi5iPaBbV5oG7fMQ0xBTKN 5wsR9dNs0CArbIsLz099/h2q0jzIzEk= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-44-s7KcRMaqOH6wPoRmPn1rGg-1; Wed, 24 Jan 2024 17:00:56 -0500 X-MC-Unique: s7KcRMaqOH6wPoRmPn1rGg-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 288DE29AA3B7; Wed, 24 Jan 2024 22:00:56 +0000 (UTC) Received: from localhost (unknown [10.39.192.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id 73054492BC6; Wed, 24 Jan 2024 22:00:55 +0000 (UTC) Date: Wed, 24 Jan 2024 17:00:54 -0500 From: Stefan Hajnoczi To: Hanna Czenczek Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Fiona Ebner , Paolo Bonzini , Kevin Wolf , "Michael S . Tsirkin" , Fam Zheng Subject: Re: [PATCH 1/2] virtio-scsi: Attach event vq notifier with no_poll Message-ID: <20240124220054.GA613094@fedora> References: <20240124173834.66320-1-hreitz@redhat.com> <20240124173834.66320-2-hreitz@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="AKxFsHwvUfu8guYx" Content-Disposition: inline In-Reply-To: <20240124173834.66320-2-hreitz@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.5, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --AKxFsHwvUfu8guYx Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Jan 24, 2024 at 06:38:29PM +0100, Hanna Czenczek wrote: > As of commit 38738f7dbbda90fbc161757b7f4be35b52205552 ("virtio-scsi: > don't waste CPU polling the event virtqueue"), we only attach an io_read > notifier for the virtio-scsi event virtqueue instead, and no polling > notifiers. During operation, the event virtqueue is typically > non-empty, but none of the buffers are intended to be used immediately. > Instead, they only get used when certain events occur. Therefore, it > makes no sense to continuously poll it when non-empty, because it is > supposed to be and stay non-empty. >=20 > We do this by using virtio_queue_aio_attach_host_notifier_no_poll() > instead of virtio_queue_aio_attach_host_notifier() for the event > virtqueue. >=20 > Commit 766aa2de0f29b657148e04599320d771c36fd126 ("virtio-scsi: implement > BlockDevOps->drained_begin()") however has virtio_scsi_drained_end() use > virtio_queue_aio_attach_host_notifier() for all virtqueues, including > the event virtqueue. This can lead to it being polled again, undoing > the benefit of commit 38738f7dbbda90fbc161757b7f4be35b52205552. >=20 > Fix it by using virtio_queue_aio_attach_host_notifier_no_poll() for the > event virtqueue. >=20 > Reported-by: Fiona Ebner > Fixes: 766aa2de0f29b657148e04599320d771c36fd126 > ("virtio-scsi: implement BlockDevOps->drained_begin()") > Signed-off-by: Hanna Czenczek > --- > hw/scsi/virtio-scsi.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) Thank you! Reviewed-by: Stefan Hajnoczi --AKxFsHwvUfu8guYx Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmWxiJUACgkQnKSrs4Gr c8hbCQf/fhI2RZoV1Db3OqSOwL5rJrXq9t/P7YSgHKA4GEPLD0iET7PCQiK1/ae1 C6X6zq8SjyBMhduyXRfeYSPuNxR1o7YWVRdwiUKo/uWmVbJyNewvVfhMgibm0u0q 3J4ZbdjBC91KFxg6+e/QkcyZwnci0kskalIFJOjC4ydizSJRY73gHpHZMptfDStF zQ44XYznN3TfQOGfBl22Y5YmTb3MW/jO/TSSEmXNJkKO2Jrpcxmy3nWoQT0cexxV 4bgI3KGr+UXjuKM3BlO+SwlTeTT3z0tU97V5OA9S8+3u/lA+f4rOvfVwV3Zq5bRl d8pIX0IVsLoqjVaElWsJen8vLJv47w== =jdXK -----END PGP SIGNATURE----- --AKxFsHwvUfu8guYx--