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Tsirkin" , Fei Li Cc: linux-kernel@vger.kernel.org, Jason Wang , Pawel Moll , Suzuki K Poulose References: <20190719133135.32418-1-lifei.shirley@bytedance.com> <20190719133135.32418-2-lifei.shirley@bytedance.com> <20190719111440-mutt-send-email-mst@kernel.org> From: Fam Zheng Message-ID: <5b29804b-528b-61bd-1ab6-4e442d360cf9@bytedance.com> Date: Mon, 22 Jul 2019 10:28:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190719111440-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/19/19 11:17 PM, Michael S. Tsirkin wrote: > On Fri, Jul 19, 2019 at 09:31:34PM +0800, Fei Li wrote: >> From: Fam Zheng >> >> This allows the backend to _not_ trap mmio read of the status register >> after injecting IRQ in the data path, which can improve the performance >> significantly by avoiding a vmexit for each interrupt. >> >> More importantly it also makes it possible for Firecracker to hook up >> virtio-mmio with vhost-net, in which case there isn't a way to implement >> proper status register handling. >> >> For a complete backend that does set either INT_CONFIG bit or INT_VRING >> bit upon generating irq, what happens hasn't changed. >> >> Signed-off-by: Fam Zheng > This has a side effect of skipping vring callbacks > if they trigger at the same time with a config > interrupt. > I don't see why this is safe. Good point! I think the block can be moved out from the else block and run unconditionally then. Fam > > >> --- >> drivers/virtio/virtio_mmio.c | 4 +--- >> 1 file changed, 1 insertion(+), 3 deletions(-) >> >> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c >> index e09edb5c5e06..9b42502b2204 100644 >> --- a/drivers/virtio/virtio_mmio.c >> +++ b/drivers/virtio/virtio_mmio.c >> @@ -295,9 +295,7 @@ static irqreturn_t vm_interrupt(int irq, void *opaque) >> if (unlikely(status & VIRTIO_MMIO_INT_CONFIG)) { >> virtio_config_changed(&vm_dev->vdev); >> ret = IRQ_HANDLED; >> - } >> - >> - if (likely(status & VIRTIO_MMIO_INT_VRING)) { >> + } else { >> spin_lock_irqsave(&vm_dev->lock, flags); >> list_for_each_entry(info, &vm_dev->virtqueues, node) >> ret |= vring_interrupt(irq, info->vq); >> -- >> 2.11.0