On Thu, Jan 06, 2022 at 08:48:59PM +0800, Xuan Zhuo wrote: > On Thu, 6 Jan 2022 07:28:31 -0500, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Fri, Oct 29, 2021 at 02:28:11PM +0800, Xuan Zhuo wrote: > > > If the VIRTIO_RING_F_INDIRECT_DESC negotiation succeeds, and the number > > > of sgs used for sending packets is greater than 1. We must constantly > > > call __kmalloc/kfree to allocate/release desc. > > > > > > So where is this going? I really like the performance boost. My concern > > is that if guest spans NUMA nodes and when handler switches from > > node to another this will keep reusing the cache from > > the old node. A bunch of ways were suggested to address this, but > > even just making the cache per numa node would help. > > > > In fact, this is the problem I encountered in implementing virtio-net to support > xdp socket. With virtqueue reset[0] has been merged into virtio spec. I > am completing this series of work. My plan is: > > 1. virtio support advance dma > 2. linux kernel/qemu support virtqueue reset > 3. virtio-net support AF_XDP > 4. virtio support cache indirect desc > > [0]: https://github.com/oasis-tcs/virtio-spec/issues/124 > > Thanks. OK it's up to you how to prioritize your work. An idea though: isn't there a way to reduce the use of indirect? Even with all the caching, it is surely not free. We made it work better in the past with: commit e7428e95a06fb516fac1308bd0e176e27c0b9287 ("virtio-net: put virtio-net header inline with data"). and commit 6ebbc1a6383fe78be3c0961d1475043ac6cc2542 virtio-net: Set needed_headroom for virtio-net when VIRTIO_F_ANY_LAYOUT is true can't something similar be done for XDP? Another idea is to skip indirect even with s/g as number of outstanding entries is small. The difficulty with this approach is that it has to be tested across a large number of configurations, including storage to make sure we don't cause regressions, unless we are very conservative and only make a small % of entries direct. Will doing that still help? It looks attractive on paper: if guest starts outpacing host and ring begins to fill up to more than say 10% then we switch to allocating indirect entries which slows guest down. > > > > > In the case of extremely fast package delivery, the overhead cannot be > > > ignored: > > > > > > 27.46% [kernel] [k] virtqueue_add > > > 16.66% [kernel] [k] detach_buf_split > > > 16.51% [kernel] [k] virtnet_xsk_xmit > > > 14.04% [kernel] [k] virtqueue_add_outbuf > > > 5.18% [kernel] [k] __kmalloc > > > 4.08% [kernel] [k] kfree > > > 2.80% [kernel] [k] virtqueue_get_buf_ctx > > > 2.22% [kernel] [k] xsk_tx_peek_desc > > > 2.08% [kernel] [k] memset_erms > > > 0.83% [kernel] [k] virtqueue_kick_prepare > > > 0.76% [kernel] [k] virtnet_xsk_run > > > 0.62% [kernel] [k] __free_old_xmit_ptr > > > 0.60% [kernel] [k] vring_map_one_sg > > > 0.53% [kernel] [k] native_apic_mem_write > > > 0.46% [kernel] [k] sg_next > > > 0.43% [kernel] [k] sg_init_table > > > 0.41% [kernel] [k] kmalloc_slab > > > > > > This patch adds a cache function to virtio to cache these allocated indirect > > > desc instead of constantly allocating and releasing desc. > > > > > > v3: > > > pre-allocate per buffer indirect descriptors array > > > > > > v2: > > > use struct list_head to cache the desc > > > > > > *** BLURB HERE *** > > > > > > Xuan Zhuo (3): > > > virtio: cache indirect desc for split > > > virtio: cache indirect desc for packed > > > virtio-net: enable virtio desc cache > > > > > > drivers/net/virtio_net.c | 11 +++ > > > drivers/virtio/virtio.c | 6 ++ > > > drivers/virtio/virtio_ring.c | 131 ++++++++++++++++++++++++++++++----- > > > include/linux/virtio.h | 14 ++++ > > > 4 files changed, 145 insertions(+), 17 deletions(-) > > > > > > -- > > > 2.31.0 > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
