From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751994AbdI1HTd (ORCPT ); Thu, 28 Sep 2017 03:19:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33004 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751548AbdI1HTb (ORCPT ); Thu, 28 Sep 2017 03:19:31 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 7ABF3E3759 Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jasowang@redhat.com Subject: Re: [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx() To: "Michael S. Tsirkin" Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1506067355-5771-1-git-send-email-jasowang@redhat.com> <1506067355-5771-4-git-send-email-jasowang@redhat.com> <20170926170047-mutt-send-email-mst@kernel.org> <20170928015749-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <76182672-9e48-101f-4e18-c2e28c87f0e8@redhat.com> Date: Thu, 28 Sep 2017 15:19:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20170928015749-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 28 Sep 2017 07:19:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017年09月28日 06:58, Michael S. Tsirkin wrote: > On Wed, Sep 27, 2017 at 08:38:24AM +0800, Jason Wang wrote: >> On 2017年09月27日 03:13, Michael S. Tsirkin wrote: >>> On Fri, Sep 22, 2017 at 04:02:33PM +0800, Jason Wang wrote: >>>> This patch introduces a helper which just increase the used idx. This >>>> will be used in pair with vhost_prefetch_desc_indices() by batching >>>> code. >>>> >>>> Signed-off-by: Jason Wang >>>> --- >>>> drivers/vhost/vhost.c | 33 +++++++++++++++++++++++++++++++++ >>>> drivers/vhost/vhost.h | 1 + >>>> 2 files changed, 34 insertions(+) >>>> >>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >>>> index 8424166d..6532cda 100644 >>>> --- a/drivers/vhost/vhost.c >>>> +++ b/drivers/vhost/vhost.c >>>> @@ -2178,6 +2178,39 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len) >>>> } >>>> EXPORT_SYMBOL_GPL(vhost_add_used); >>>> +int vhost_add_used_idx(struct vhost_virtqueue *vq, int n) >>>> +{ >>>> + u16 old, new; >>>> + >>>> + old = vq->last_used_idx; >>>> + new = (vq->last_used_idx += n); >>>> + /* If the driver never bothers to signal in a very long while, >>>> + * used index might wrap around. If that happens, invalidate >>>> + * signalled_used index we stored. TODO: make sure driver >>>> + * signals at least once in 2^16 and remove this. >>>> + */ >>>> + if (unlikely((u16)(new - vq->signalled_used) < (u16)(new - old))) >>>> + vq->signalled_used_valid = false; >>>> + >>>> + /* Make sure buffer is written before we update index. */ >>>> + smp_wmb(); >>>> + if (vhost_put_user(vq, cpu_to_vhost16(vq, vq->last_used_idx), >>>> + &vq->used->idx)) { >>>> + vq_err(vq, "Failed to increment used idx"); >>>> + return -EFAULT; >>>> + } >>>> + if (unlikely(vq->log_used)) { >>>> + /* Log used index update. */ >>>> + log_write(vq->log_base, >>>> + vq->log_addr + offsetof(struct vring_used, idx), >>>> + sizeof(vq->used->idx)); >>>> + if (vq->log_ctx) >>>> + eventfd_signal(vq->log_ctx, 1); >>>> + } >>>> + return 0; >>>> +} >>>> +EXPORT_SYMBOL_GPL(vhost_add_used_idx); >>>> + >>>> static int __vhost_add_used_n(struct vhost_virtqueue *vq, >>>> struct vring_used_elem *heads, >>>> unsigned count) >>>> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h >>>> index 16c2cb6..5dd6c05 100644 >>>> --- a/drivers/vhost/vhost.h >>>> +++ b/drivers/vhost/vhost.h >>>> @@ -199,6 +199,7 @@ int __vhost_get_vq_desc(struct vhost_virtqueue *vq, >>>> void vhost_discard_vq_desc(struct vhost_virtqueue *, int n); >>>> int vhost_vq_init_access(struct vhost_virtqueue *); >>>> +int vhost_add_used_idx(struct vhost_virtqueue *vq, int n); >>>> int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len); >>>> int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads, >>>> unsigned count); >>> Please change the API to hide the fact that there's an index that needs >>> to be updated. >> In fact, an interesting optimization on top is just call >> vhost_add_used_idx(vq, n) instead of n vhost_add_used_idx(vq, 1). That's the >> reason I leave n in the API. >> >> Thanks > Right but you could increment some internal counter in the vq > structure then update the used index using some api > with a generic name, e.g. add_used_complete or something like this. > Right, I see. Thanks