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 E0145ECAAA3 for ; Fri, 26 Aug 2022 03:10:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244684AbiHZDKC convert rfc822-to-8bit (ORCPT ); Thu, 25 Aug 2022 23:10:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244434AbiHZDJ5 (ORCPT ); Thu, 25 Aug 2022 23:09:57 -0400 Received: from smtp236.sjtu.edu.cn (smtp236.sjtu.edu.cn [202.120.2.236]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EEB5E1031; Thu, 25 Aug 2022 20:09:49 -0700 (PDT) Received: from mta90.sjtu.edu.cn (unknown [10.118.0.90]) by smtp236.sjtu.edu.cn (Postfix) with ESMTPS id C08E21008B389; Fri, 26 Aug 2022 11:09:42 +0800 (CST) Received: from localhost (localhost.localdomain [127.0.0.1]) by mta90.sjtu.edu.cn (Postfix) with ESMTP id A7D3B37C894; Fri, 26 Aug 2022 11:09:42 +0800 (CST) X-Virus-Scanned: amavisd-new at Received: from mta90.sjtu.edu.cn ([127.0.0.1]) by localhost (mta90.sjtu.edu.cn [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id lA8wrcseUiVS; Fri, 26 Aug 2022 11:09:42 +0800 (CST) Received: from mstore105.sjtu.edu.cn (mstore101.sjtu.edu.cn [10.118.0.105]) by mta90.sjtu.edu.cn (Postfix) with ESMTP id 7978A37C893; Fri, 26 Aug 2022 11:09:42 +0800 (CST) Date: Fri, 26 Aug 2022 11:09:42 +0800 (CST) From: Guo Zhi To: jasowang Cc: eperezma , sgarzare , Michael Tsirkin , netdev , linux-kernel , kvm list , virtualization Message-ID: <1347002628.9092578.1661483382423.JavaMail.zimbra@sjtu.edu.cn> In-Reply-To: <3a184162-afdc-9103-e786-66d796389e3a@redhat.com> References: <20220817135718.2553-1-qtxuning1999@sjtu.edu.cn> <20220817135718.2553-2-qtxuning1999@sjtu.edu.cn> <3a184162-afdc-9103-e786-66d796389e3a@redhat.com> Subject: Re: [RFC v2 1/7] vhost: expose used buffers MIME-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 8BIT X-Originating-IP: [10.166.246.247] X-Mailer: Zimbra 8.8.15_GA_4308 (ZimbraWebClient - GC104 (Mac)/8.8.15_GA_3928) Thread-Topic: vhost: expose used buffers Thread-Index: ELzt12WtjSRXgoL62yzDeHlxV1NK/w== Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org ----- Original Message ----- > From: "jasowang" > To: "Guo Zhi" , "eperezma" , "sgarzare" , "Michael > Tsirkin" > Cc: "netdev" , "linux-kernel" , "kvm list" , > "virtualization" > Sent: Thursday, August 25, 2022 3:01:31 PM > Subject: Re: [RFC v2 1/7] vhost: expose used buffers > ÔÚ 2022/8/17 21:57, 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 | 14 ++++++++++++-- >> drivers/vhost/vhost.h | 1 + >> 2 files changed, 13 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >> index 40097826cff0..7b20fa5a46c3 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]; > > > Do we need to check whether or not the buffer is fully used before doing > this? > This is the caller / user of __vhost_add_used_n's duty to make sure all buffer is fully used. The device will only batch if all heads are fully used. > >> + } >> 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; >> } >> @@ -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)) { >> r = __vhost_add_used_n(vq, heads, n); >> if (r < 0) >> return r; >> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h >> index d9109107af08..0d5c49a30421 100644 >> --- a/drivers/vhost/vhost.h >> +++ b/drivers/vhost/vhost.h >> @@ -236,6 +236,7 @@ enum { >> VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) | >> (1ULL << VIRTIO_RING_F_INDIRECT_DESC) | >> (1ULL << VIRTIO_RING_F_EVENT_IDX) | >> + (1ULL << VIRTIO_F_IN_ORDER) | >> (1ULL << VHOST_F_LOG_ALL) | > > > Are we sure all vhost devices can support in-order (especially the SCSI)? > > It looks better to start from a device specific one. > > Thanks > Sorry for my mistake, I will change it. > >> (1ULL << VIRTIO_F_ANY_LAYOUT) | >> (1ULL << VIRTIO_F_VERSION_1)