From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC PATCH V3 1/5] vhost: generalize adding used elem Date: Fri, 4 Jan 2019 16:29:34 -0500 Message-ID: <20190104162857-mutt-send-email-mst@kernel.org> References: <20181229124656.3900-1-jasowang@redhat.com> <20181229124656.3900-2-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <20181229124656.3900-2-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sat, Dec 29, 2018 at 08:46:52PM +0800, Jason Wang wrote: > Use one generic vhost_copy_to_user() instead of two dedicated > accessor. This will simplify the conversion to fine grain > accessors. About 2% improvement of PPS were seen during vitio-user > txonly test. > > Signed-off-by: Jason Wang I don't hve a problem with this patch but do you have any idea how come removing what's supposed to be an optimization speeds things up? > --- > drivers/vhost/vhost.c | 11 +---------- > 1 file changed, 1 insertion(+), 10 deletions(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 55e5aa662ad5..f179b5ee14c4 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -2174,16 +2174,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq, > > start = vq->last_used_idx & (vq->num - 1); > used = vq->used->ring + start; > - if (count == 1) { > - if (vhost_put_user(vq, heads[0].id, &used->id)) { > - vq_err(vq, "Failed to write used id"); > - return -EFAULT; > - } > - if (vhost_put_user(vq, heads[0].len, &used->len)) { > - vq_err(vq, "Failed to write used len"); > - return -EFAULT; > - } > - } else if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) { > + if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) { > vq_err(vq, "Failed to write used"); > return -EFAULT; > } > -- > 2.17.1