From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753503AbeDSRqT (ORCPT ); Thu, 19 Apr 2018 13:46:19 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:53842 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752924AbeDSRqS (ORCPT ); Thu, 19 Apr 2018 13:46:18 -0400 Date: Thu, 19 Apr 2018 20:46:17 +0300 From: "Michael S. Tsirkin" To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, Ohad Ben-Cohen , Bjorn Andersson , linux-remoteproc@vger.kernel.org, Jason Wang , virtualization@lists.linux-foundation.org Subject: Re: [PATCH] virtio_ring: switch to dma_XX barriers for rpmsg Message-ID: <20180419204017-mutt-send-email-mst@kernel.org> References: <1524159181-351878-1-git-send-email-mst@redhat.com> <5047d08c-9f9e-2902-d425-1fac849ce5b4@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5047d08c-9f9e-2902-d425-1fac849ce5b4@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 19, 2018 at 07:39:21PM +0200, Paolo Bonzini wrote: > On 19/04/2018 19:35, Michael S. Tsirkin wrote: > > virtio is using barriers to order memory accesses, thus > > dma_wmb/rmb is a good match. > > > > Build-tested on x86: Before > > > > [mst@tuck linux]$ size drivers/virtio/virtio_ring.o > > text data bss dec hex filename > > 11392 820 0 12212 2fb4 drivers/virtio/virtio_ring.o > > > > After > > mst@tuck linux]$ size drivers/virtio/virtio_ring.o > > text data bss dec hex filename > > 11284 820 0 12104 2f48 drivers/virtio/virtio_ring.o > > > > Cc: Ohad Ben-Cohen > > Cc: Bjorn Andersson > > Cc: linux-remoteproc@vger.kernel.org > > Signed-off-by: Michael S. Tsirkin > > --- > > > > It's good in theory, but could one of RPMSG maintainers please review > > and ack this patch? Or even better test it? > > > > All these barriers are useless on Intel anyway ... > > This should be okay, but I wonder if there should be a virtio_wmb(...) > or an "if (weak_barriers) wmb()" before the "writel" in vm_notify > (drivers/virtio/virtio_mmio.c). > > Thanks, > > Paolo That one uses weak barriers AFAIK. IIUC you mean rproc_virtio_notify. I suspect it works because specific kick callbacks have a barrier internally. > > > > include/linux/virtio_ring.h | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h > > index bbf3252..fab0213 100644 > > --- a/include/linux/virtio_ring.h > > +++ b/include/linux/virtio_ring.h > > @@ -35,7 +35,7 @@ static inline void virtio_rmb(bool weak_barriers) > > if (weak_barriers) > > virt_rmb(); > > else > > - rmb(); > > + dma_rmb(); > > } > > > > static inline void virtio_wmb(bool weak_barriers) > > @@ -43,7 +43,7 @@ static inline void virtio_wmb(bool weak_barriers) > > if (weak_barriers) > > virt_wmb(); > > else > > - wmb(); > > + dma_wmb(); > > } > > > > static inline void virtio_store_mb(bool weak_barriers, > >