From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH (repost) RFC 2/2] virtio-pci: recall and return msix notifications on ISR read Date: Thu, 3 Nov 2011 14:07:13 +0200 Message-ID: <20111103120712.GE18296@redhat.com> References: <6dc9aa9764b1cfddf557a98f269e0f7d31ce03ac.1320259840.git.mst@redhat.com> <4EB27E3F.2030503@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <4EB27E3F.2030503@siemens.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Jan Kiszka Cc: Anthony Liguori , "qemu-devel@nongnu.org" , "virtualization@lists.linux-foundation.org" , Blue Swirl , Stefan Weil , Avi Kivity , Richard Henderson List-Id: virtualization@lists.linuxfoundation.org On Thu, Nov 03, 2011 at 12:42:55PM +0100, Jan Kiszka wrote: > On 2011-11-02 21:11, Michael S. Tsirkin wrote: > > MSIX spec requires that device can be operated with > > all vectors masked, by polling pending bits. > > Add APIs to recall an msix notification, and make polling > > mode possible in virtio-pci by clearing the > > pending bits and setting ISR appropriately on ISR read. > > > > Signed-off-by: Michael S. Tsirkin > > --- > > hw/msix.c | 26 ++++++++++++++++++++++++++ > > hw/msix.h | 3 +++ > > hw/virtio-pci.c | 11 ++++++++++- > > 3 files changed, 39 insertions(+), 1 deletions(-) > > > > diff --git a/hw/msix.c b/hw/msix.c > > index 63b41b9..fe967c9 100644 > > --- a/hw/msix.c > > +++ b/hw/msix.c > > @@ -349,6 +349,32 @@ void msix_notify(PCIDevice *dev, unsigned vector) > > stl_le_phys(address, data); > > } > > > > +/* Recall outstanding MSI-X notifications for a vector, if possible. > > + * Return true if any were outstanding. */ > > +bool msix_recall(PCIDevice *dev, unsigned vector) > > +{ > > + bool ret; > > + if (vector >= dev->msix_entries_nr) > > + return false; > > + ret = msix_is_pending(dev, vector); > > + msix_clr_pending(dev, vector); > > + return ret; > > +} > > I would prefer to have a single API instead to clarify the tight relation: > > bool msi[x]_set_notify(PCIDevice *dev, unsigned vector, unsigned level) > > Would return true for level=1 if the message was either sent directly or > queued (we could deliver false if it was already queued, but I see no > use case for this yet). It's a matter of taste: some people like functions with flags, some prefer separate functions. I really prefer two functions. But I agree it woulkd be better to have a name that makes it clear that what we recall is a notification. msix_notify_queue/msix_notify_dequeue? > Also, I don't see the generic value of some msix_recall_all. I think > it's better handled in a single loop over all vectors at caller site, > clearing the individual interrupt reason bits on a per-vector basis > there. msix_recall_all is only useful in the virtio case where you have > one vector of reason A and all the rest of B. Once you had multiple > reason C vectors as well, it would not help anymore. > > Jan The reason I wanted to have it is to reduce the overhead this adds: since PBA is packed, it's much faster to check whether any bits are set than by going through them all, one by one. Typically all PBA bits are clear ... I agree it might not help non-virtio devices, but to me it looks like a harmless little helper - what's the issue with it? > -- > Siemens AG, Corporate Technology, CT T DE IT 1 > Corporate Competence Center Embedded Linux