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Date: Sun, 11 May 2008 14:14:06 +0100 From: "Daniel J Blueman" <daniel.blueman@...il.com> To: axboe@...nel.dk Cc: "Linux Kernel" <linux-kernel@...r.kernel.org>, Matthew <jackdachef@...il.com> Subject: Re: performance "regression" in cfq compared to anticipatory, deadline and noop I've been experiencing this for a while also; an almost 50% regression is seen for single-process reads (ie sync) if slice_idle is 1ms or more (eg default of 8) [1], which seems phenomenal. Jens, is this the expected price to pay for optimal busy-spindle scheduling, a design issue, bug or am I missing something totally? Thanks, Daniel --- [1] # cat /sys/block/sda/queue/iosched/slice_idle 8 # echo 1 >/proc/sys/vm/drop_caches # dd if=/dev/sda of=/dev/null bs=64k count=5000 5000+0 records in 5000+0 records out 327680000 bytes (328 MB) copied, 4.92922 s, 66.5 MB/s # echo 0 >/sys/block/sda/queue/iosched/slice_idle # echo 1 >/proc/sys/vm/drop_caches # dd if=/dev/sda of=/dev/null bs=64k count=5000 5000+0 records in 5000+0 records out 327680000 bytes (328 MB) copied, 2.74098 s, 120 MB/s # hdparm -Tt /dev/sda /dev/sda: Timing cached reads: 15464 MB in 2.00 seconds = 7741.05 MB/sec Timing buffered disk reads: 342 MB in 3.01 seconds = 113.70 MB/sec [120MB/s is known platter-rate for this disc, so expected] -- Daniel J Blueman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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