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Tsirkin" To: Jason Wang Cc: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, maz@kernel.org, tglx@linutronix.de, peterz@infradead.org, sgarzare@redhat.com, keirf@google.com Subject: Re: [PATCH 1/3] virtio: use virtio_device_ready() in virtio_device_restore() Message-ID: <20220324064205-mutt-send-email-mst@kernel.org> References: <20220324084004.14349-1-jasowang@redhat.com> <20220324084004.14349-2-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220324084004.14349-2-jasowang@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 24, 2022 at 04:40:02PM +0800, Jason Wang wrote: > From: Stefano Garzarella > > This avoids setting DRIVER_OK twice for those drivers that call > virtio_device_ready() in the .restore Is this trying to say it's faster? If yes this one looks like a red herring. Yes we skip a write but we replace it with a read which is not better performance-wise. If we want to optimize this, it is better to just do that inside virtio_add_status: diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c index 75c8d560bbd3..cd943c31bdbb 100644 --- a/drivers/virtio/virtio.c +++ b/drivers/virtio/virtio.c @@ -161,8 +161,14 @@ static void virtio_config_enable(struct virtio_device *dev) void virtio_add_status(struct virtio_device *dev, unsigned int status) { + unsigned int device_status; + might_sleep(); - dev->config->set_status(dev, dev->config->get_status(dev) | status); + + device_status = dev->config->get_status(dev); + + if (status & ~device_status) + dev->config->set_status(dev, device_status | status); } EXPORT_SYMBOL_GPL(virtio_add_status); > and it will allows us to do > extension on virtio_device_ready() without duplicating codes. > > Signed-off-by: Stefano Garzarella > Signed-off-by: Jason Wang > --- > drivers/virtio/virtio.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > index 22f15f444f75..75c8d560bbd3 100644 > --- a/drivers/virtio/virtio.c > +++ b/drivers/virtio/virtio.c > @@ -526,8 +526,9 @@ int virtio_device_restore(struct virtio_device *dev) > goto err; > } > > - /* Finally, tell the device we're all set */ > - virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK); > + /* If restore didn't do it, mark device DRIVER_OK ourselves. */ I preferred the original comment, it said why we are doing this, new one repeats what code is doing. > + if (!(dev->config->get_status(dev) & VIRTIO_CONFIG_S_DRIVER_OK)) > + virtio_device_ready(dev); > > virtio_config_enable(dev); > > -- > 2.25.1