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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7722CC54EE9 for ; Thu, 8 Sep 2022 08:43:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231524AbiIHInw convert rfc822-to-8bit (ORCPT ); Thu, 8 Sep 2022 04:43:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230092AbiIHInt (ORCPT ); Thu, 8 Sep 2022 04:43:49 -0400 Received: from smtp237.sjtu.edu.cn (smtp237.sjtu.edu.cn [202.120.2.237]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 594BCA1D5E; Thu, 8 Sep 2022 01:43:47 -0700 (PDT) Received: from mta91.sjtu.edu.cn (unknown [10.118.0.91]) by smtp237.sjtu.edu.cn (Postfix) with ESMTPS id 2116E1007FEC5; Thu, 8 Sep 2022 16:43:43 +0800 (CST) Received: from localhost (localhost.localdomain [127.0.0.1]) by mta91.sjtu.edu.cn (Postfix) with ESMTP id B80A537C842; Thu, 8 Sep 2022 16:43:43 +0800 (CST) X-Virus-Scanned: amavisd-new at Received: from mta91.sjtu.edu.cn ([127.0.0.1]) by localhost (mta91.sjtu.edu.cn [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id OyaMGIvmIgAn; Thu, 8 Sep 2022 16:43:43 +0800 (CST) Received: from mstore105.sjtu.edu.cn (mstore101.sjtu.edu.cn [10.118.0.105]) by mta91.sjtu.edu.cn (Postfix) with ESMTP id 8AF6E37C840; Thu, 8 Sep 2022 16:43:43 +0800 (CST) Date: Thu, 8 Sep 2022 16:43:43 +0800 (CST) From: Guo Zhi To: jasowang Cc: eperezma , sgarzare , Michael Tsirkin , netdev , linux-kernel , kvm list , virtualization Message-ID: <1852578160.165892.1662626623503.JavaMail.zimbra@sjtu.edu.cn> In-Reply-To: References: <20220901055434.824-1-qtxuning1999@sjtu.edu.cn> <20220901055434.824-2-qtxuning1999@sjtu.edu.cn> Subject: Re: [RFC v3 1/7] vhost: expose used buffers MIME-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 8BIT X-Originating-IP: [10.162.206.161] X-Mailer: Zimbra 8.8.15_GA_4372 (ZimbraWebClient - GC104 (Mac)/8.8.15_GA_3928) Thread-Topic: vhost: expose used buffers Thread-Index: fByL794dn6QpX8lgbNrQBzAr5HjJEQ== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- Original Message ----- > From: "jasowang" > To: "Guo Zhi" , "eperezma" , "sgarzare" , "Michael > Tsirkin" > Cc: "netdev" , "linux-kernel" , "kvm list" , > "virtualization" > Sent: Wednesday, September 7, 2022 12:21:06 PM > Subject: Re: [RFC v3 1/7] vhost: expose used buffers > ÔÚ 2022/9/1 13:54, Guo Zhi дµÀ: >> Follow VIRTIO 1.1 spec, only writing out a single used ring for a batch >> of descriptors. >> >> Signed-off-by: Guo Zhi >> --- >> drivers/vhost/vhost.c | 16 +++++++++++++--- >> 1 file changed, 13 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >> index 40097826cff0..26862c8bf751 100644 >> --- a/drivers/vhost/vhost.c >> +++ b/drivers/vhost/vhost.c >> @@ -2376,10 +2376,20 @@ static int __vhost_add_used_n(struct vhost_virtqueue >> *vq, >> vring_used_elem_t __user *used; >> u16 old, new; >> int start; >> + int copy_n = count; >> >> + /** >> + * If in order feature negotiated, devices can notify the use of a batch of >> buffers to >> + * the driver by only writing out a single used ring entry with the id >> corresponding >> + * to the head entry of the descriptor chain describing the last buffer in the >> batch. >> + */ >> + if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) { >> + copy_n = 1; >> + heads = &heads[count - 1]; >> + } > > > Would it better to have a dedicated helper like > vhost_add_used_in_order() here? > That would be much more convenient and clear to implement. I think have a dedicated function for in order feature in vhost is better. > > >> start = vq->last_used_idx & (vq->num - 1); >> used = vq->used->ring + start; >> - if (vhost_put_used(vq, heads, start, count)) { >> + if (vhost_put_used(vq, heads, start, copy_n)) { >> vq_err(vq, "Failed to write used"); >> return -EFAULT; >> } >> @@ -2388,7 +2398,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq, >> smp_wmb(); >> /* Log used ring entry write. */ >> log_used(vq, ((void __user *)used - (void __user *)vq->used), >> - count * sizeof *used); >> + copy_n * sizeof(*used)); >> } >> old = vq->last_used_idx; >> new = (vq->last_used_idx += count); >> @@ -2410,7 +2420,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct >> vring_used_elem *heads, >> >> start = vq->last_used_idx & (vq->num - 1); >> n = vq->num - start; >> - if (n < count) { >> + if (n < count && !vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) { > > > This seems strange, any reason for this? (Actually if we support > in-order we only need one used slot which fit for the case here) > > Thanks > If in order feature negotiated, even the count is larger than n, we don't need to call __vhost_add_used_n again, because in order only use one slot. Thanks > >> r = __vhost_add_used_n(vq, heads, n); >> if (r < 0) >> return r;