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authorHisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>2009-12-18 00:27:26 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-18 00:45:32 +0100
commit65a80b4c61f5b5f6eb0f5669c8fb120893bfb388 (patch)
tree44136f7130ad0a1074502afbfdf8b93efe35976e /kernel
parentrtc: set wakeup capability for I2C and SPI RTC drivers (diff)
downloadlinux-65a80b4c61f5b5f6eb0f5669c8fb120893bfb388.tar.xz
linux-65a80b4c61f5b5f6eb0f5669c8fb120893bfb388.zip
readahead: add blk_run_backing_dev
I added blk_run_backing_dev on page_cache_async_readahead so readahead I/O is unpluged to improve throughput on especially RAID environment. The normal case is, if page N become uptodate at time T(N), then T(N) <= T(N+1) holds. With RAID (and NFS to some degree), there is no strict ordering, the data arrival time depends on runtime status of individual disks, which breaks that formula. So in do_generic_file_read(), just after submitting the async readahead IO request, the current page may well be uptodate, so the page won't be locked, and the block device won't be implicitly unplugged: if (PageReadahead(page)) page_cache_async_readahead() if (!PageUptodate(page)) goto page_not_up_to_date; //... page_not_up_to_date: lock_page_killable(page); Therefore explicit unplugging can help. Following is the test result with dd. #dd if=testdir/testfile of=/dev/null bs=16384 -2.6.30-rc6 1048576+0 records in 1048576+0 records out 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s -2.6.30-rc6-patched 1048576+0 records in 1048576+0 records out 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s (7Disks RAID-0 Array) -2.6.30-rc6 1054976+0 records in 1054976+0 records out 17284726784 bytes (17 GB) copied, 212.233 seconds, 81.4 MB/s -2.6.30-rc6-patched 1054976+0 records out 17284726784 bytes (17 GB) copied, 198.878 seconds, 86.9 MB/s (7Disks RAID-5 Array) The patch was found to improve performance with the SCST scsi target driver. See http://sourceforge.net/mailarchive/forum.php?thread_name=a0272b440906030714g67eabc5k8f847fb1e538cc62%40mail.gmail.com&forum_name=scst-devel [akpm@linux-foundation.org: unbust comment layout] [akpm@linux-foundation.org: "fix" CONFIG_BLOCK=n] Signed-off-by: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp> Acked-by: Wu Fengguang <fengguang.wu@intel.com> Cc: Jens Axboe <jens.axboe@oracle.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Tested-by: Ronald <intercommit@gmail.com> Cc: Bart Van Assche <bart.vanassche@gmail.com> Cc: Vladislav Bolkhovitin <vst@vlnb.net> Cc: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
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