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authorMagnus Karlsson <magnus.karlsson@intel.com>2019-08-14 10:27:17 +0300
committerDaniel Borkmann <daniel@iogearbox.net>2019-08-18 00:07:32 +0300
commit77cd0d7b3f257fd0e3096b4fdcff1a7d38e99e10 (patch)
treea4cfb41db704798731fd18261d171b1b75fc0bfa /include/uapi/linux/if_xdp.h
parent9116e5e2b1fff71dce501d971e86a3695acc3dba (diff)
downloadlinux-77cd0d7b3f257fd0e3096b4fdcff1a7d38e99e10.tar.xz
xsk: add support for need_wakeup flag in AF_XDP rings
This commit adds support for a new flag called need_wakeup in the AF_XDP Tx and fill rings. When this flag is set, it means that the application has to explicitly wake up the kernel Rx (for the bit in the fill ring) or kernel Tx (for bit in the Tx ring) processing by issuing a syscall. Poll() can wake up both depending on the flags submitted and sendto() will wake up tx processing only. The main reason for introducing this new flag is to be able to efficiently support the case when application and driver is executing on the same core. Previously, the driver was just busy-spinning on the fill ring if it ran out of buffers in the HW and there were none on the fill ring. This approach works when the application is running on another core as it can replenish the fill ring while the driver is busy-spinning. Though, this is a lousy approach if both of them are running on the same core as the probability of the fill ring getting more entries when the driver is busy-spinning is zero. With this new feature the driver now sets the need_wakeup flag and returns to the application. The application can then replenish the fill queue and then explicitly wake up the Rx processing in the kernel using the syscall poll(). For Tx, the flag is only set to one if the driver has no outstanding Tx completion interrupts. If it has some, the flag is zero as it will be woken up by a completion interrupt anyway. As a nice side effect, this new flag also improves the performance of the case where application and driver are running on two different cores as it reduces the number of syscalls to the kernel. The kernel tells user space if it needs to be woken up by a syscall, and this eliminates many of the syscalls. This flag needs some simple driver support. If the driver does not support this, the Rx flag is always zero and the Tx flag is always one. This makes any application relying on this feature default to the old behaviour of not requiring any syscalls in the Rx path and always having to call sendto() in the Tx path. For backwards compatibility reasons, this feature has to be explicitly turned on using a new bind flag (XDP_USE_NEED_WAKEUP). I recommend that you always turn it on as it so far always have had a positive performance impact. The name and inspiration of the flag has been taken from io_uring by Jens Axboe. Details about this feature in io_uring can be found in http://kernel.dk/io_uring.pdf, section 8.3. Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com> Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'include/uapi/linux/if_xdp.h')
-rw-r--r--include/uapi/linux/if_xdp.h13
1 files changed, 13 insertions, 0 deletions
diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
index faaa5ca2a117..62b80d57b72a 100644
--- a/include/uapi/linux/if_xdp.h
+++ b/include/uapi/linux/if_xdp.h
@@ -16,6 +16,15 @@
#define XDP_SHARED_UMEM (1 << 0)
#define XDP_COPY (1 << 1) /* Force copy-mode */
#define XDP_ZEROCOPY (1 << 2) /* Force zero-copy mode */
+/* If this option is set, the driver might go sleep and in that case
+ * the XDP_RING_NEED_WAKEUP flag in the fill and/or Tx rings will be
+ * set. If it is set, the application need to explicitly wake up the
+ * driver with a poll() (Rx and Tx) or sendto() (Tx only). If you are
+ * running the driver and the application on the same core, you should
+ * use this option so that the kernel will yield to the user space
+ * application.
+ */
+#define XDP_USE_NEED_WAKEUP (1 << 3)
struct sockaddr_xdp {
__u16 sxdp_family;
@@ -25,10 +34,14 @@ struct sockaddr_xdp {
__u32 sxdp_shared_umem_fd;
};
+/* XDP_RING flags */
+#define XDP_RING_NEED_WAKEUP (1 << 0)
+
struct xdp_ring_offset {
__u64 producer;
__u64 consumer;
__u64 desc;
+ __u64 flags;
};
struct xdp_mmap_offsets {