{"push_id":637522064,"size":1,"distinct_size":1,"ref":"refs/heads/air","head":"b892f389e8082c7c8fb8b4fb580c2a37d10f688f","before":"58cff63ddabf7ecc236af2128ce0fa164b5558c5","commits":[{"sha":"b892f389e8082c7c8fb8b4fb580c2a37d10f688f","author":{"email":"f39834d3f313de4aa8a5483c1e8a76e8299c5a6b@gmail.com","name":"klozz"},"message":" readahead: make context readahead more conservative\n\nThis helps performance on moderately dense random reads on\nSSD.\n\nTransaction-Per-Second numbers provided by Taobao:\n\n  QPS case\n\n-------------------------------------------------------\n  7536 disable\ncontext readahead totally\nw/ patch: 7129 slower size rampup and start RA\non the 3rd read\n  6717 slower size rampup\nw/o patch: 5581 unmodified\ncontext readahead\n\nBefore, readahead will be started whenever reading\npage N+1 when it happen\nto read N recently.  After patch, we'll only\nstart readahead when *three*\nrandom reads happen to access pages N, N+1,\nN+2.  The probability of this\nhappening is extremely low for pure random\nreads, unless they are very\ndense, which actually deserves some\nreadahead.\n\nAlso start with a smaller readahead window.  The impact to\ninterleaved\nsequential reads should be small, because for a long run\nstream, the the\nsmall readahead window rampup phase is negletable.\n\nThe\ncontext readahead actually benefits clustered random reads on HDD\nwhose\nseek cost is pretty high.  However as SSD is increasingly used\nfor\nrandom read workloads it's better for the context readahead to\nconcentrate\non interleaved sequential reads.\n\nAnother SSD rand read test\nfrom Miao\n\n        # file size:        2GB\n        # read IO amount:\n625MB\n        sysbench --test=fileio          \\\n\n--max-requests=10000    \\\n                --num-threads=1         \\\n\n--file-num=1            \\\n                --file-block-size=64K   \\\n\n--file-test-mode=rndrd  \\\n                --file-fsync-freq=0     \\\n\n--file-fsync-end=off    run\n\nshows the performance of btrfs grows up\nfrom 69MB/s to 121MB/s, ext4 from\n104MB/s to 121MB/s.\n\nChange-Id: Ia0f58b36611db01234f715e1e04bbf09344ba2d0\nSigned-off-by: klozz <xxx.reptar.rawrr.xxx@gmail.com>","distinct":true,"url":"https://api.github.com/repos/fozzil4/android_kernel_motorola_msm8226/commits/b892f389e8082c7c8fb8b4fb580c2a37d10f688f"}]}