Jens Axboe <[email protected]> wrote:{ > >> > >>>Some more investigation - it appears to be broken read-ahead, actually. > >>> > >>>--- mm/readahead.c~ 2005-07-08 11:16:14.000000000 +0200 > >>>+++ mm/readahead.c 2005-07-08 11:17:49.000000000 +0200 > >>>@@ -351,7 +351,9 @@ > >>> ra->cache_hit += nr_to_read; > >>> if (ra->cache_hit >= VM_MAX_CACHE_HIT) { > >>> ra_off(ra); > >>>+#if 0 > >>> ra->flags |= RA_FLAG_INCACHE; > >>>+#endif > >>> return 0; > >>> } > >>> } else { > >> > >> >Just use the test app I posted, it shows the problem just fine. If I > >use a regular file, behaviour is identical as expected (ie equally > >broken :-). } Modified test app shows comparison w/ and w/o O_DIRECT. Your comments please! 2.4.31# (hdparm -f /dev/hda;free;time /tmp/readisk /dev/hda 1 ) /dev/hda: total used free shared buffers cached Mem: 256388 23728 232660 0 1944 4324 -/+ buffers/cache: 17460 238928 Swap: 0 0 0 Mem Throughput: 107 MiB/sec - 8388608-16 bs-blks Mem Throughput: 121 MiB/sec - 4194304-32 bs-blks Mem Throughput: 122 MiB/sec - 2097152-64 bs-blks Mem Throughput: 122 MiB/sec - 1048576-128 bs-blks Mem Throughput: 120 MiB/sec - 524288-256 bs-blks Mem Throughput: 120 MiB/sec - 262144-512 bs-blks Mem Throughput: 131 MiB/sec - 131072-1024 bs-blks Mem Throughput: 336 MiB/sec - 65536-2048 bs-blks Mem Throughput: 476 MiB/sec - 32768-4096 bs-blks Mem Throughput: 432 MiB/sec - 16384-8192 bs-blks Mem Throughput: 824 MiB/sec - 8192-16384 bs-blks <--- 20% faster Mem Throughput: 799 MiB/sec - 4096-32768 bs-blks Mem Throughput: 494 MiB/sec - 2048-65536 bs-blks Mem Throughput: 270 MiB/sec - 1024-131072 bs-blks Mem Throughput: 146 MiB/sec - 512-262144 bs-blks Mem Throughput: 76 MiB/sec - 256-524288 bs-blks Disk Throughput: 39 MiB/sec 1.13user 12.35system 0:15.65elapsed 86%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (87major+2061minor)pagefaults 0swaps ===================================================================== 2.4.31# (hdparm -f /dev/hda;free;time /tmp/readisk /dev/hda 1 1 ) O_DIRECT /dev/hda: total used free shared buffers cached Mem: 256388 23824 232564 0 2024 4324 -/+ buffers/cache: 17476 238912 Swap: 0 0 0 Mem Throughput: 36 MiB/sec - 8388608-16 bs-blks Mem Throughput: 34 MiB/sec - 4194304-32 bs-blks Mem Throughput: 34 MiB/sec - 2097152-64 bs-blks Mem Throughput: 37 MiB/sec - 1048576-128 bs-blks Mem Throughput: 29 MiB/sec - 524288-256 bs-blks <--- small dip Mem Throughput: 15 MiB/sec - 262144-512 bs-blks <--- 333% slower Mem Throughput: 42 MiB/sec - 131072-1024 bs-blks Mem Throughput: 45 MiB/sec - 65536-2048 bs-blks Mem Throughput: 40 MiB/sec - 32768-4096 bs-blks Mem Throughput: 36 MiB/sec - 16384-8192 bs-blks Mem Throughput: 33 MiB/sec - 8192-16384 bs-blks Mem Throughput: 25 MiB/sec - 4096-32768 bs-blks Mem Throughput: 16 MiB/sec - 2048-65536 bs-blks Mem Throughput: 10 MiB/sec - 1024-131072 bs-blks read infile: Invalid argument 512-262144 bs-blks <--- too small? read infile: Invalid argument 256-524288 bs-blks Disk Throughput: 38 MiB/sec 0.27user 10.88system 1:12.95elapsed 15%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (99major+2062minor)pagefaults 0swaps ===================================================================== 2.6.12# (hdparm -f /dev/hda;free;time /tmp/readisk /dev/hda 1 ) /dev/hda: total used free shared buffers cached Mem: 255228 15668 239560 0 5060 4252 -/+ buffers/cache: 6356 248872 Swap: 0 0 0 Mem Throughput: 97 MiB/sec - 8388608-16 bs-blks Mem Throughput: 120 MiB/sec - 4194304-32 bs-blks Mem Throughput: 120 MiB/sec - 2097152-64 bs-blks Mem Throughput: 120 MiB/sec - 1048576-128 bs-blks Mem Throughput: 121 MiB/sec - 524288-256 bs-blks Mem Throughput: 120 MiB/sec - 262144-512 bs-blks Mem Throughput: 129 MiB/sec - 131072-1024 bs-blks Mem Throughput: 237 MiB/sec - 65536-2048 bs-blks Mem Throughput: 451 MiB/sec - 32768-4096 bs-blks Mem Throughput: 418 MiB/sec - 16384-8192 bs-blks Mem Throughput: 636 MiB/sec - 8192-16384 bs-blks Mem Throughput: 672 MiB/sec - 4096-32768 bs-blks <--- 20% slower Mem Throughput: 399 MiB/sec - 2048-65536 bs-blks Mem Throughput: 217 MiB/sec - 1024-131072 bs-blks Mem Throughput: 115 MiB/sec - 512-262144 bs-blks Mem Throughput: 59 MiB/sec - 256-524288 bs-blks Disk Throughput: 26 MiB/sec 0.93user 13.79system 0:18.59elapsed 79%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+2150minor)pagefaults 0swaps ===================================================================== 2.6.12# (hdparm -f /dev/hda;free;time /tmp/readisk /dev/hda 1 1) O_DIRECT /dev/hda: total used free shared buffers cached Mem: 255228 15668 239560 0 5060 4252 -/+ buffers/cache: 6356 248872 Swap: 0 0 0 Mem Throughput: 33 MiB/sec - 8388608-16 bs-blks Mem Throughput: 30 MiB/sec - 4194304-32 bs-blks Mem Throughput: 34 MiB/sec - 2097152-64 bs-blks Mem Throughput: 39 MiB/sec - 1048576-128 bs-blks Mem Throughput: 30 MiB/sec - 524288-256 bs-blks <--- small dip Mem Throughput: 49 MiB/sec - 262144-512 bs-blks <--- 333% faster Mem Throughput: 49 MiB/sec - 131072-1024 bs-blks Mem Throughput: 44 MiB/sec - 65536-2048 bs-blks Mem Throughput: 42 MiB/sec - 32768-4096 bs-blks Mem Throughput: 40 MiB/sec - 16384-8192 bs-blks Mem Throughput: 29 MiB/sec - 8192-16384 bs-blks Mem Throughput: 22 MiB/sec - 4096-32768 bs-blks Mem Throughput: 14 MiB/sec - 2048-65536 bs-blks Mem Throughput: 8 MiB/sec - 1024-131072 bs-blks Mem Throughput: 4 MiB/sec - 512-262144 bs-blks read infile: Invalid argument 256-524288 bs-blks <--- too small? Disk Throughput: 34 MiB/sec 0.69user 32.09system 1:39.15elapsed 33%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+2164minor)pagefaults 0swaps =====================================================================
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- From: Jens Axboe <[email protected]>
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