skips ring accesses but drops out of order support At high level this follows alf design https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/alf_queue.c but on most (single-threaded) benchmarks this seems to be slower than the layout without index use. Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> --- tools/virtio/ringtest/virtio_ring_0_9.c | 49 ++++++++++++++++++++++++++++- tools/virtio/ringtest/virtio_ring_inorder.c | 2 ++ tools/virtio/ringtest/Makefile | 4 ++- 3 files changed, 53 insertions(+), 2 deletions(-) create mode 100644 tools/virtio/ringtest/virtio_ring_inorder.c diff --git a/tools/virtio/ringtest/virtio_ring_0_9.c b/tools/virtio/ringtest/virtio_ring_0_9.c index 47c9a1a..7618662 100644 --- a/tools/virtio/ringtest/virtio_ring_0_9.c +++ b/tools/virtio/ringtest/virtio_ring_0_9.c @@ -26,6 +26,14 @@ struct vring ring; * high bits of ring id ^ 0x8000). */ /* #ifdef RING_POLL */ +/* enabling the below activates experimental in-order code + * (which skips ring updates and reads and writes len in descriptor). + */ +/* #ifdef INORDER */ + +#if defined(RING_POLL) && defined(INORDER) +#error "RING_POLL and INORDER are mutually exclusive" +#endif /* how much padding is needed to avoid false cache sharing */ #define HOST_GUEST_PADDING 0x80 @@ -35,7 +43,11 @@ struct guest { unsigned short last_used_idx; unsigned short num_free; unsigned short kicked_avail_idx; +#ifndef INORDER unsigned short free_head; +#else + unsigned short reserved_free_head; +#endif unsigned char reserved[HOST_GUEST_PADDING - 10]; } guest; @@ -66,8 +78,10 @@ void alloc_ring(void) guest.avail_idx = 0; guest.kicked_avail_idx = -1; guest.last_used_idx = 0; +#ifndef INORDER /* Put everything in free lists. */ guest.free_head = 0; +#endif for (i = 0; i < ring_size - 1; i++) ring.desc[i].next = i + 1; host.used_idx = 0; @@ -84,13 +98,20 @@ void alloc_ring(void) /* guest side */ int add_inbuf(unsigned len, void *buf, void *datap) { - unsigned head, avail; + unsigned head; +#ifndef INORDER + unsigned avail; +#endif struct vring_desc *desc; if (!guest.num_free) return -1; +#ifdef INORDER + head = (ring_size - 1) & (guest.avail_idx++); +#else head = guest.free_head; +#endif guest.num_free--; desc = ring.desc; @@ -102,7 +123,9 @@ int add_inbuf(unsigned len, void *buf, void *datap) * descriptors. */ desc[head].flags &= ~VRING_DESC_F_NEXT; +#ifndef INORDER guest.free_head = desc[head].next; +#endif data[head].data = datap; @@ -113,8 +136,12 @@ int add_inbuf(unsigned len, void *buf, void *datap) ring.avail->ring[avail & (ring_size - 1)] = (head | (avail & ~(ring_size - 1))) ^ 0x8000; #else +#ifndef INORDER + /* Barrier A (for pairing) */ + smp_release(); avail = (ring_size - 1) & (guest.avail_idx++); ring.avail->ring[avail] = head; +#endif /* Barrier A (for pairing) */ smp_release(); #endif @@ -141,15 +168,27 @@ void *get_buf(unsigned *lenp, void **bufp) return NULL; /* Barrier B (for pairing) */ smp_acquire(); +#ifdef INORDER + head = (ring_size - 1) & guest.last_used_idx; + index = head; +#else head = (ring_size - 1) & guest.last_used_idx; index = ring.used->ring[head].id; #endif + +#endif +#ifdef INORDER + *lenp = ring.desc[index].len; +#else *lenp = ring.used->ring[head].len; +#endif datap = data[index].data; *bufp = (void*)(unsigned long)ring.desc[index].addr; data[index].data = NULL; +#ifndef INORDER ring.desc[index].next = guest.free_head; guest.free_head = index; +#endif guest.num_free++; guest.last_used_idx++; return datap; @@ -283,16 +322,24 @@ bool use_buf(unsigned *lenp, void **bufp) smp_acquire(); used_idx &= ring_size - 1; +#ifdef INORDER + head = used_idx; +#else head = ring.avail->ring[used_idx]; +#endif desc = &ring.desc[head]; #endif *lenp = desc->len; *bufp = (void *)(unsigned long)desc->addr; +#ifdef INORDER + desc->len = desc->len - 1; +#else /* now update used ring */ ring.used->ring[used_idx].id = head; ring.used->ring[used_idx].len = desc->len - 1; +#endif /* Barrier B (for pairing) */ smp_release(); host.used_idx++; diff --git a/tools/virtio/ringtest/virtio_ring_inorder.c b/tools/virtio/ringtest/virtio_ring_inorder.c new file mode 100644 index 0000000..2438ca5 --- /dev/null +++ b/tools/virtio/ringtest/virtio_ring_inorder.c @@ -0,0 +1,2 @@ +#define INORDER 1 +#include "virtio_ring_0_9.c" diff --git a/tools/virtio/ringtest/Makefile b/tools/virtio/ringtest/Makefile index feaa64a..8037971 100644 --- a/tools/virtio/ringtest/Makefile +++ b/tools/virtio/ringtest/Makefile @@ -1,6 +1,6 @@ all: -all: ring virtio_ring_0_9 virtio_ring_poll +all: ring virtio_ring_0_9 virtio_ring_poll virtio_ring_inorder CFLAGS += -Wall CFLAGS += -pthread -O2 -ggdb @@ -13,10 +13,12 @@ virtio_ring_poll.o: virtio_ring_poll.c virtio_ring_0_9.c main.h ring: ring.o main.o virtio_ring_0_9: virtio_ring_0_9.o main.o virtio_ring_poll: virtio_ring_poll.o main.o +virtio_ring_inorder: virtio_ring_inorder.o main.o clean: -rm main.o -rm ring.o ring -rm virtio_ring_0_9.o virtio_ring_0_9 -rm virtio_ring_poll.o virtio_ring_poll + -rm virtio_ring_inorder.o virtio_ring_inorder .PHONY: all clean -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
