On Saturday, May 07, 2016 04:44:51 PM Slawa Olhovchenkov wrote: > On Fri, May 06, 2016 at 05:52:15PM -0700, John Baldwin wrote: > > > On Saturday, May 07, 2016 12:33:35 AM John Baldwin wrote: > > > Author: jhb > > > Date: Sat May 7 00:33:35 2016 > > > New Revision: 299210 > > > URL: https://svnweb.freebsd.org/changeset/base/299210 > > > > > > Log: > > > Use DDP to implement zerocopy TCP receive with aio_read(). > > > > > > Chelsio's TCP offload engine supports direct DMA of received TCP payload > > > into wired user buffers. This feature is known as Direct-Data > > > Placement. > > > However, to scale well the adapter needs to prepare buffers for DDP > > > before data arrives. aio_read() is more amenable to this requirement > > > than > > > read() as applications often call read() only after data is available in > > > the socket buffer. > > > > > > When DDP is enabled, TOE sockets use the recently added pru_aio_queue > > > protocol hook to claim aio_read(2) requests instead of letting them use > > > the default AIO socket logic. The DDP feature supports scheduling DMA > > > to two buffers at a time so that the second buffer is ready for use > > > after the first buffer is filled. The aio/DDP code optimizes the case > > > of an application ping-ponging between two buffers (similar to the > > > zero-copy bpf(4) code) by keeping the two most recently used AIO buffers > > > wired. If a buffer is reused, the aio/DDP code is able to reuse the > > > vm_page_t array as well as page pod mappings (a kind of MMU mapping the > > > Chelsio NIC uses to describe user buffers). The generation of the > > > vmspace of the calling process is used in conjunction with the user > > > buffer's address and length to determine if a user buffer matches a > > > previously used buffer. If an application queues a buffer for AIO that > > > does not match a previously used buffer then the least recently used > > > buffer is unwired before the new buffer is wired. This ensures that no > > > more than two user buffers per socket are ever wired. > > > > > > Note that this feature is best suited to applications sending a steady > > > stream of data vs short bursts of traffic. > > > > > > Discussed with: np > > > Relnotes: yes > > > Sponsored by: Chelsio Communications > > > > The primary tool I used for evaluating performance was netperf's TCP stream > > test. It is a best case for this (constant stream of traffic), but that is > > also the intended use case for this feature. > > > > Using 2 64K buffers in a ping-pong via aio_read() to receive a 40Gbps stream > > used about about two full CPUs (~190% CPU usage) on a single-package > > Intel E5-1620 v3 @ 3.50GHz with the stock TCP stack. Enabling TOE brings > > the > > usage down to about 110% CPU. With DDP, the usage is around 30% of a single > > CPU. With two 1MB buffers the the stock and TOE numbers are about the same, > > but the DDP usage is about 5% of single CPU. > > > > Note that these numbers are with aio_read(). read() fares a bit better > > (180% > > for stock and 70% for TOE). Before the AIO rework, trying to use aio_read() > > with two buffers in a ping-pong used twice as much CPU as bare read(), but > > aio_read() in general is now fairly comparable to read() at least in terms > > of > > CPU overhead. > > Can be this impovement of nfsclient and etc?
The NFS client is implemented in the kernel (and doesn't use the AIO interfaces), so that would be a bit trickier to manage. OTOH, this could be useful for something like rsync if that had an opton to use aio_read(). -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
