On 5/6/22 5:26 PM, Jens Axboe wrote: > On 5/6/22 4:23 PM, Jens Axboe wrote: >> On 5/6/22 1:00 AM, Hao Xu wrote: >>> Let multishot support multishot mode, currently only add accept as its >>> first comsumer. >>> theoretical analysis: >>> 1) when connections come in fast >>> - singleshot: >>> add accept sqe(userpsace) --> accept inline >>> ^ | >>> |-----------------| >>> - multishot: >>> add accept sqe(userspace) --> accept inline >>> ^ | >>> |--*--| >>> >>> we do accept repeatedly in * place until get EAGAIN >>> >>> 2) when connections come in at a low pressure >>> similar thing like 1), we reduce a lot of userspace-kernel context >>> switch and useless vfs_poll() >>> >>> >>> tests: >>> Did some tests, which goes in this way: >>> >>> server client(multiple) >>> accept connect >>> read write >>> write read >>> close close >>> >>> Basically, raise up a number of clients(on same machine with server) to >>> connect to the server, and then write some data to it, the server will >>> write those data back to the client after it receives them, and then >>> close the connection after write return. Then the client will read the >>> data and then close the connection. Here I test 10000 clients connect >>> one server, data size 128 bytes. And each client has a go routine for >>> it, so they come to the server in short time. >>> test 20 times before/after this patchset, time spent:(unit cycle, which >>> is the return value of clock()) >>> before: >>> 1930136+1940725+1907981+1947601+1923812+1928226+1911087+1905897+1941075 >>> +1934374+1906614+1912504+1949110+1908790+1909951+1941672+1969525+1934984 >>> +1934226+1914385)/20.0 = 1927633.75 >>> after: >>> 1858905+1917104+1895455+1963963+1892706+1889208+1874175+1904753+1874112 >>> +1874985+1882706+1884642+1864694+1906508+1916150+1924250+1869060+1889506 >>> +1871324+1940803)/20.0 = 1894750.45 >>> >>> (1927633.75 - 1894750.45) / 1927633.75 = 1.65% >>> >>> >>> A liburing test is here: >>> https://github.com/HowHsu/liburing/blob/multishot_accept/test/accept.c >> >> Wish I had seen that, I wrote my own! But maybe that's good, you tend to >> find other issues through that. >> >> Anyway, works for me in testing, and I can see this being a nice win for >> accept intensive workloads. I pushed a bunch of cleanup patches that >> should just get folded in. Can you fold them into your patches and >> address the other feedback, and post a v3? I pushed the test branch >> here: >> >> https://git.kernel.dk/cgit/linux-block/log/?h=fastpoll-mshot > > Quick benchmark here, accepting 10k connections: > > Stock kernel > real 0m0.728s > user 0m0.009s > sys 0m0.192s > > Patched > real 0m0.684s > user 0m0.018s > sys 0m0.102s > > Looks like a nice win for a highly synthetic benchmark. Nothing > scientific, was just curious. One more thought on this - how is it supposed to work with accept-direct? One idea would be to make it incrementally increasing. But we need a good story for that, if it's exclusive to non-direct files, then it's a lot less interesting as the latter is really nice win for lots of files. If we can combine the two, even better. -- Jens Axboe
