On Tue, 11 Jan 2022 10:44:52 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote: > On Mon, Jan 10, 2022 at 5:29 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote: > > > > On Mon, 10 Jan 2022 16:54:58 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > On Mon, Jan 10, 2022 at 3:59 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote: > > > > > > > > On Mon, 10 Jan 2022 15:41:27 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > > > On Mon, Jan 10, 2022 at 3:24 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > On Mon, 10 Jan 2022 14:43:39 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > 在 2022/1/7 下午2:33, Xuan Zhuo 写道: > > > > > > > > In the scenario where indirect is not used, each desc corresponds to an > > > > > > > > extra, which is used to record information such as dma, flags, and > > > > > > > > next. > > > > > > > > > > > > > > > > In the scenario of using indirect, the assigned desc does not have the > > > > > > > > corresponding extra record dma information, and the dma information must > > > > > > > > be obtained from the desc when unmap. > > > > > > > > > > > > > > > > This patch allocates the corresponding extra array when indirect desc is > > > > > > > > allocated. This has these advantages: > > > > > > > > 1. Record the dma information of desc, no need to read desc when unmap > > > > > > > > 2. It will be more convenient and unified in processing > > > > > > > > 3. Some additional information can be recorded in extra, which will be > > > > > > > > used in subsequent patches. > > > > > > > > > > > > > > > > > > > > > Two questions: > > > > > > > > > > > > > > 1) Is there any performance number for this change? I guess it gives > > > > > > > more stress on the cache. > > > > > > > > > > > > I will add performance test data in the next version. > > > > > > > > > > > > > 2) Is there a requirement to mix the pre mapped sg with unmapped sg? If > > > > > > > not, a per virtqueue flag looks sufficient > > > > > > > > > > > > There is this requirement. For example, in the case of AF_XDP, a patcket > > > > > > contains two parts, one is virtio_net_hdr, and the other is the actual data > > > > > > packet from AF_XDP. The former is unmapped sg, and the latter is pre mapped sg. > > > > > > > > > > Any chance to map virtio_net_hdr() manually by AF_XDP routine in this case? > > > > > > > > Well, it is indeed possible to do so. In the indirect scenario, we can record it > > > > in vring->split.desc_extra[head].flags > > > > > > > > Then we have to agree that there can be no mixed situation. > > > > > > I think it would be easier and less performance regression if we don't > > > do huge changes in the core unless it's a must. > > > > > > > Ok, I plan to add two new interface virtqueue_add_outbuf_flag(), > > virtqueue_add_inbuf_flag() pass a flag parameter to virtqueue_add() to > > mark sgs addr is predma. > > > > I don't want to use sg->dma_address, so we have to check whether each sg uses > > dma_address. If it is not unified, we will also handle exception. > > > > > Btw, I forgot the conclusion of the last AF_XDP series. Why is it > > > better to change virtio_ring instead of AF_XDP (which seems easier). > > > > Regarding this question, I'm guessing you mean to make AF_XDP not use DMA > > addresses? Instead pass virtual addresses to virtio. > > > > It would certainly be simpler, but I think there is a performance gain in doing > > the DMA mapping ahead of time. > > Any reason for this? Is it just because AF_XDP did batch mapping? > AF_XDP completes all DMA maps during initialization, and virtio currently executes a DMA map every time virtqueue_add() is executed. If we support advance DMA, there will be no DMA overhead every time virtqueue_add() is executed. > Actually there's another subtle difference, AF_XDP tends to use > DMA_BIDIRECTIONAL but the virtio_ring map depends on the in/out. Yes. Thanks. > > Thanks > > > > > Thanks. > > > > > > > > > > Thanks > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
