From patchwork Wed Jan 24 17:38:29 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hanna Czenczek X-Patchwork-Id: 13529503 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 554EDC47E49 for ; Wed, 24 Jan 2024 17:39:53 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rShD5-00029L-IQ; Wed, 24 Jan 2024 12:38:47 -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 1rShD3-00028B-KP for qemu-devel@nongnu.org; Wed, 24 Jan 2024 12:38:45 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rShD2-00026z-2h for qemu-devel@nongnu.org; Wed, 24 Jan 2024 12:38:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1706117923; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=F4OmqxgKC3qddtr32VKeaMZ3RM6Vrl6zAhR61NVpNCM=; b=SOZ/p14nmRwFi6jS8elXJlNOuV7ba79pcKy9fvRz+z8jgIZzhr8Xdm/ZP8xgeJLfRqikpq R3ZJvXuRMsrP776nUcDQ0YkBbIcTRZMB9nC/PPchm3cHygpsXLEj5YI4wB1YEb7dScQ4ZM bzU0cDTAdtkFim5Gf3WzFMhhTPQEWCk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-301-kvcE8gPUMZuwz-zrv7iZqA-1; Wed, 24 Jan 2024 12:38:39 -0500 X-MC-Unique: kvcE8gPUMZuwz-zrv7iZqA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (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 3576F845DC9; Wed, 24 Jan 2024 17:38:39 +0000 (UTC) Received: from localhost (unknown [10.39.194.82]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BCDF0C0FDCA; Wed, 24 Jan 2024 17:38:38 +0000 (UTC) From: Hanna Czenczek To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Hanna Czenczek , Stefan Hajnoczi , Fiona Ebner , Paolo Bonzini , Kevin Wolf , "Michael S . Tsirkin" , Fam Zheng Subject: [PATCH 1/2] virtio-scsi: Attach event vq notifier with no_poll Date: Wed, 24 Jan 2024 18:38:29 +0100 Message-ID: <20240124173834.66320-2-hreitz@redhat.com> In-Reply-To: <20240124173834.66320-1-hreitz@redhat.com> References: <20240124173834.66320-1-hreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.129.124; envelope-from=hreitz@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_H4=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=ham 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 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. 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. 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. Fix it by using virtio_queue_aio_attach_host_notifier_no_poll() for the event virtqueue. Reported-by: Fiona Ebner Fixes: 766aa2de0f29b657148e04599320d771c36fd126 ("virtio-scsi: implement BlockDevOps->drained_begin()") Signed-off-by: Hanna Czenczek Reviewed-by: Stefan Hajnoczi Tested-by: Fiona Ebner Reviewed-by: Fiona Ebner --- hw/scsi/virtio-scsi.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index 690aceec45..9f02ceea09 100644 --- a/hw/scsi/virtio-scsi.c +++ b/hw/scsi/virtio-scsi.c @@ -1149,6 +1149,7 @@ static void virtio_scsi_drained_begin(SCSIBus *bus) static void virtio_scsi_drained_end(SCSIBus *bus) { VirtIOSCSI *s = container_of(bus, VirtIOSCSI, bus); + VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s); VirtIODevice *vdev = VIRTIO_DEVICE(s); uint32_t total_queues = VIRTIO_SCSI_VQ_NUM_FIXED + s->parent_obj.conf.num_queues; @@ -1166,7 +1167,11 @@ static void virtio_scsi_drained_end(SCSIBus *bus) for (uint32_t i = 0; i < total_queues; i++) { VirtQueue *vq = virtio_get_queue(vdev, i); - virtio_queue_aio_attach_host_notifier(vq, s->ctx); + if (vq == vs->event_vq) { + virtio_queue_aio_attach_host_notifier_no_poll(vq, s->ctx); + } else { + virtio_queue_aio_attach_host_notifier(vq, s->ctx); + } } } From patchwork Wed Jan 24 17:38:30 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hanna Czenczek X-Patchwork-Id: 13529504 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 50E4BC46CD2 for ; Wed, 24 Jan 2024 17:39:53 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rShD9-0002CP-CS; Wed, 24 Jan 2024 12:38:51 -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 1rShD7-00029k-0t for qemu-devel@nongnu.org; Wed, 24 Jan 2024 12:38:49 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rShD5-00027f-93 for qemu-devel@nongnu.org; Wed, 24 Jan 2024 12:38:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1706117926; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=lX1sT80RAiQermXgE8doojql21JqoxTeFTn7oKC4pDU=; b=PPpC/2RudlqsK56uhlJFIxqIshKVKdcqSeuJObTur5Q5tm/6l4DhKXB9Jl/H4nPagdJPYj Hpve+k8d3hC3ODG6arBeWidqrlFpkvwlnrOj8bsLvM3HeCaPrNPyscusHxM6c05ZvOCAf9 zjhBOPB/9WIuepogTxqW7dbP5bhT9RE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-433-mhbvCd6RPu6cq5HFJL0nbQ-1; Wed, 24 Jan 2024 12:38:41 -0500 X-MC-Unique: mhbvCd6RPu6cq5HFJL0nbQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (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 55EA4845E60; Wed, 24 Jan 2024 17:38:41 +0000 (UTC) Received: from localhost (unknown [10.39.194.82]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E4E182028CD2; Wed, 24 Jan 2024 17:38:40 +0000 (UTC) From: Hanna Czenczek To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Hanna Czenczek , Stefan Hajnoczi , Fiona Ebner , Paolo Bonzini , Kevin Wolf , "Michael S . Tsirkin" , Fam Zheng Subject: [PATCH 2/2] virtio: Keep notifications disabled during drain Date: Wed, 24 Jan 2024 18:38:30 +0100 Message-ID: <20240124173834.66320-3-hreitz@redhat.com> In-Reply-To: <20240124173834.66320-1-hreitz@redhat.com> References: <20240124173834.66320-1-hreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=hreitz@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_H4=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 During drain, we do not care about virtqueue notifications, which is why we remove the handlers on it. When removing those handlers, whether vq notifications are enabled or not depends on whether we were in polling mode or not; if not, they are enabled (by default); if so, they have been disabled by the io_poll_start callback. Because we do not care about those notifications after removing the handlers, this is fine. However, we have to explicitly ensure they are enabled when re-attaching the handlers, so we will resume receiving notifications. We do this in virtio_queue_aio_attach_host_notifier*(). If such a function is called while we are in a polling section, attaching the notifiers will then invoke the io_poll_start callback, re-disabling notifications. Because we will always miss virtqueue updates in the drained section, we also need to poll the virtqueue once after attaching the notifiers. Buglink: https://issues.redhat.com/browse/RHEL-3934 Signed-off-by: Hanna Czenczek Tested-by: Fiona Ebner Reviewed-by: Fiona Ebner Reviewed-by: Stefan Hajnoczi --- include/block/aio.h | 7 ++++++- hw/virtio/virtio.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+), 1 deletion(-) diff --git a/include/block/aio.h b/include/block/aio.h index 5d0a114988..8378553eb9 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -480,9 +480,14 @@ void aio_set_event_notifier(AioContext *ctx, AioPollFn *io_poll, EventNotifierHandler *io_poll_ready); -/* Set polling begin/end callbacks for an event notifier that has already been +/* + * Set polling begin/end callbacks for an event notifier that has already been * registered with aio_set_event_notifier. Do nothing if the event notifier is * not registered. + * + * Note that if the io_poll_end() callback (or the entire notifier) is removed + * during polling, it will not be called, so an io_poll_begin() is not + * necessarily always followed by an io_poll_end(). */ void aio_set_event_notifier_poll(AioContext *ctx, EventNotifier *notifier, diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 7549094154..4166da9e97 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -3556,6 +3556,17 @@ static void virtio_queue_host_notifier_aio_poll_end(EventNotifier *n) void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx) { + /* + * virtio_queue_aio_detach_host_notifier() can leave notifications disabled. + * Re-enable them. (And if detach has not been used before, notifications + * being enabled is still the default state while a notifier is attached; + * see virtio_queue_host_notifier_aio_poll_end(), which will always leave + * notifications enabled once the polling section is left.) + */ + if (!virtio_queue_get_notification(vq)) { + virtio_queue_set_notification(vq, 1); + } + aio_set_event_notifier(ctx, &vq->host_notifier, virtio_queue_host_notifier_read, virtio_queue_host_notifier_aio_poll, @@ -3563,6 +3574,13 @@ void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx) aio_set_event_notifier_poll(ctx, &vq->host_notifier, virtio_queue_host_notifier_aio_poll_begin, virtio_queue_host_notifier_aio_poll_end); + + /* + * We will have ignored notifications about new requests from the guest + * during the drain, so "kick" the virt queue to process those requests + * now. + */ + virtio_queue_notify(vq->vdev, vq->queue_index); } /* @@ -3573,14 +3591,38 @@ void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx) */ void virtio_queue_aio_attach_host_notifier_no_poll(VirtQueue *vq, AioContext *ctx) { + /* See virtio_queue_aio_attach_host_notifier() */ + if (!virtio_queue_get_notification(vq)) { + virtio_queue_set_notification(vq, 1); + } + aio_set_event_notifier(ctx, &vq->host_notifier, virtio_queue_host_notifier_read, NULL, NULL); + + /* + * See virtio_queue_aio_attach_host_notifier(). + * Note that this may be unnecessary for the type of virtqueues this + * function is used for. Still, it will not hurt to have a quick look into + * whether we can/should process any of the virtqueue elements. + */ + virtio_queue_notify(vq->vdev, vq->queue_index); } void virtio_queue_aio_detach_host_notifier(VirtQueue *vq, AioContext *ctx) { aio_set_event_notifier(ctx, &vq->host_notifier, NULL, NULL, NULL); + + /* + * aio_set_event_notifier_poll() does not guarantee whether io_poll_end() + * will run after io_poll_begin(), so by removing the notifier, we do not + * know whether virtio_queue_host_notifier_aio_poll_end() has run after a + * previous virtio_queue_host_notifier_aio_poll_begin(), i.e. whether + * notifications are enabled or disabled. It does not really matter anyway; + * we just removed the notifier, so we do not care about notifications until + * we potentially re-attach it. The attach_host_notifier functions will + * ensure that notifications are enabled again when they are needed. + */ } void virtio_queue_host_notifier_read(EventNotifier *n)