From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: performance bug in virtio net xdp Date: Wed, 6 May 2020 07:57:41 -0400 Message-ID: <20200506075719-mutt-send-email-mst@kernel.org> References: <20200506035704-mutt-send-email-mst@kernel.org> <7d801479-5572-0031-b306-a735ca4ce0e4@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <7d801479-5572-0031-b306-a735ca4ce0e4@redhat.com> Sender: netdev-owner@vger.kernel.org To: Jason Wang Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Jesper Dangaard Brouer , Eugenio Perez Martin List-Id: virtualization@lists.linuxfoundation.org On Wed, May 06, 2020 at 04:37:41PM +0800, Jason Wang wrote: > > On 2020/5/6 下午4:08, Michael S. Tsirkin wrote: > > So for mergeable bufs, we use ewma machinery to guess the correct buffer > > size. If we don't guess correctly, XDP has to do aggressive copies. > > > > Problem is, xdp paths do not update the ewma at all, except > > sometimes with XDP_PASS. So whatever we happen to have > > before we attach XDP, will mostly stay around. > > > It looks ok to me since we always use PAGE_SIZE when XDP is enabled in > get_mergeable_buf_len()? > > Thanks > Oh right. Good point! Answered in another thread. > > > > The fix is probably to update ewma unconditionally. > >