Messages in this thread | | | Date | Sun, 8 May 2022 00:01:31 +0800 | Subject | Re: [PATCH v2 0/5] fast poll multishot mode | From | Hao Xu <> |
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在 2022/5/7 上午11:08, Jens Axboe 写道: > On 5/6/22 8:33 PM, Jens Axboe wrote: >> 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. > > Running some quick testing, on an actual test box (previous numbers were > from a vm on my laptop): > > Testing singleshot, normal files > Did 10000 accepts > > ________________________________________________________ > Executed in 216.10 millis fish external > usr time 9.32 millis 150.00 micros 9.17 millis > sys time 110.06 millis 67.00 micros 109.99 millis > > Testing multishot, fixed files > Did 10000 accepts > > ________________________________________________________ > Executed in 189.04 millis fish external > usr time 11.86 millis 159.00 micros 11.71 millis > sys time 93.71 millis 70.00 micros 93.64 millis > > That's about ~19 usec to accept a connection, pretty decent. Using > singleshot and with fixed files, it shaves about ~8% off, ends at around > 200msec. > > I think we can get away with using fixed files and multishot, attaching I'm not following, do you mean we shouldn't do the multishot+fixed file or we should use multishot+fixed to make the result better? > the quick patch I did below to test it. We need something better than Sorry Jens, I didn't see the quick patch, is there anything I misunderstand? > this, otherwise once the space fills up, we'll likely end up with a > sparse space and the naive approach of just incrementing the next slot > won't work at all.
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