{"push_id":1327174194,"size":1,"distinct_size":1,"ref":"refs/heads/marshmallow-6.0.1-release-lux","head":"7243f3f3bda9c8597c32ab7cc194504b00f1bde5","before":"eb8b6486461295ef800bb993ea1dbe546a0014ba","commits":[{"sha":"7243f3f3bda9c8597c32ab7cc194504b00f1bde5","author":{"name":"Fengguang Wu","email":"939d6ed212bd8093f5d268d487d459ba642d1603@intel.com"},"message":"readahead: make context readahead more conservative\n\nThis helps performance on moderately dense random reads on SSD.\n\nTransaction-Per-Second numbers provided by Taobao:\n\n\t\tQPS\tcase\n\t\t-------------------------------------------------------\n\t\t7536\tdisable context readahead totally\nw/ patch:\t7129\tslower size rampup and start RA on the 3rd read\n\t\t6717\tslower size rampup\nw/o patch:\t5581\tunmodified context readahead\n\nBefore, readahead will be started whenever reading page N+1 when it happen\nto read N recently.  After patch, we'll only start readahead when *three*\nrandom reads happen to access pages N, N+1, N+2.  The probability of this\nhappening is extremely low for pure random reads, unless they are very\ndense, which actually deserves some readahead.\n\nAlso start with a smaller readahead window.  The impact to interleaved\nsequential reads should be small, because for a long run stream, the the\nsmall readahead window rampup phase is negletable.\n\nThe context readahead actually benefits clustered random reads on HDD\nwhose seek cost is pretty high.  However as SSD is increasingly used for\nrandom read workloads it's better for the context readahead to concentrate\non interleaved sequential reads.\n\nAnother SSD rand read test from Miao\n\n        # file size:        2GB\n        # read IO amount: 625MB\n        sysbench --test=fileio          \\\n                --max-requests=10000    \\\n                --num-threads=1         \\\n                --file-num=1            \\\n                --file-block-size=64K   \\\n                --file-test-mode=rndrd  \\\n                --file-fsync-freq=0     \\\n                --file-fsync-end=off    run\n\nshows the performance of btrfs grows up from 69MB/s to 121MB/s, ext4 from\n104MB/s to 121MB/s.\n\nSigned-off-by: Wu Fengguang <fengguang.wu@intel.com>\nTested-by: Tao Ma <tm@tao.ma>\nTested-by: Miao Xie <miaox@cn.fujitsu.com>\nSigned-off-by: Andrew Morton <akpm@linux-foundation.org>\nSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>\nSigned-off-by: flar2 <asegaert@gmail.com>","distinct":true,"url":"https://api.github.com/repos/UncleKuttan/kernel-msm/commits/7243f3f3bda9c8597c32ab7cc194504b00f1bde5"}]}
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