From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.codeaurora.org by pdx-caf-mail.web.codeaurora.org (Dovecot) with LMTP id q5CUJP3/GFufEwAAmS7hNA ; Thu, 07 Jun 2018 09:50:53 +0000 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 80C0D607F7; Thu, 7 Jun 2018 09:50:53 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on pdx-caf-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by smtp.codeaurora.org (Postfix) with ESMTP id 0943C601C3; Thu, 7 Jun 2018 09:50:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 0943C601C3 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753649AbeFGJuu (ORCPT + 25 others); Thu, 7 Jun 2018 05:50:50 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49934 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753082AbeFGJut (ORCPT ); Thu, 7 Jun 2018 05:50:49 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 795CBC12BA; Thu, 7 Jun 2018 09:50:43 +0000 (UTC) Received: from [10.72.12.43] (ovpn-12-43.pek2.redhat.com [10.72.12.43]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0271820357CA; Thu, 7 Jun 2018 09:50:35 +0000 (UTC) Subject: Re: [RFC v6 4/5] virtio_ring: add event idx support in packed ring To: Tiwei Bie , mst@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Cc: wexu@redhat.com, jfreimann@redhat.com References: <20180605074046.20709-1-tiwei.bie@intel.com> <20180605074046.20709-5-tiwei.bie@intel.com> From: Jason Wang Message-ID: Date: Thu, 7 Jun 2018 17:50:32 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180605074046.20709-5-tiwei.bie@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Thu, 07 Jun 2018 09:50:48 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Thu, 07 Jun 2018 09:50:48 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'jasowang@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018年06月05日 15:40, Tiwei Bie wrote: > static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > + u16 bufs, used_idx, wrap_counter; > > START_USE(vq); > > /* We optimistically turn back on interrupts, then check if there was > * more to do. */ > + /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to > + * either clear the flags bit or point the event index at the next > + * entry. Always update the event index to keep code simple. */ > + Maybe for packed ring, it's time to treat event index separately to avoid a virtio_wmb() for event idx is off. > + /* TODO: tune this threshold */ > + if (vq->next_avail_idx < vq->last_used_idx) > + bufs = (vq->vring_packed.num + vq->next_avail_idx - > + vq->last_used_idx) * 3 / 4; > + else > + bufs = (vq->next_avail_idx - vq->last_used_idx) * 3 / 4; vq->next_avail-idx could be equal to vq->last_usd_idx when the ring is full. Though virito-net is the only user now and it can guarantee this won't happen. But consider this is a core API, we should make sure it can work for any cases. It looks to me that bufs is just vq->vring_packed.num - vq->num_free? > + > + wrap_counter = vq->used_wrap_counter; > + > + used_idx = vq->last_used_idx + bufs; > + if (used_idx >= vq->vring_packed.num) { > + used_idx -= vq->vring_packed.num; > + wrap_counter ^= 1; > + } > + > + vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev, > + used_idx | (wrap_counter << 15)); > > if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > - vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > + /* We need to update event offset and event wrap > + * counter first before updating event flags. */ > + virtio_wmb(vq->weak_barriers); > + vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC : > + VRING_EVENT_F_ENABLE; > vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > vq->event_flags_shadow); > - /* We need to enable interrupts first before re-checking > - * for more used buffers. */ > - virtio_mb(vq->weak_barriers); > } > > + /* We need to update event suppression structure first > + * before re-checking for more used buffers. */ > + virtio_mb(vq->weak_barriers); > + > if (more_used_packed(vq)) { > END_USE(vq); > return false; I think what we need to to make sure the descriptor used_idx is used? Otherwise we may stop and restart qdisc too frequently? Thanks > --