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<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>LKML: WU Fengguang: Adaptive read-ahead: benchmarks</title><link href="/css/message.css" rel="stylesheet" type="text/css" /><link href="/css/wrap.css" rel="alternate stylesheet" type="text/css" title="wrap" /><link href="/css/nowrap.css" rel="stylesheet" type="text/css" title="nowrap" /><link href="/favicon.ico" rel="shortcut icon" /><script src="/js/simple-calendar.js" type="text/javascript"></script><script src="/js/styleswitcher.js" type="text/javascript"></script><link rel="alternate" type="application/rss+xml" title="lkml.org : last 100 messages" href="/rss.php" /><link rel="alternate" type="application/rss+xml" title="lkml.org : last messages by WU Fengguang" href="/groupie.php?aid=22635" /><script> var _paq = window._paq = window._paq || []; /* tracker methods like "setCustomDimension" should be called before "trackPageView" */ _paq.push(["setDoNotTrack", true]); _paq.push(["disableCookies"]); _paq.push(['trackPageView']); _paq.push(['enableLinkTracking']); (function() { var u="//m.lkml.org/"; _paq.push(['setTrackerUrl', u+'matomo.php']); _paq.push(['setSiteId', '1']); var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0]; g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s); })(); </script></head><body onload="es.jasper.simpleCalendar.init();" itemscope="itemscope" itemtype="http://schema.org/BlogPosting"><table border="0" cellpadding="0" cellspacing="0"><tr><td width="180" align="center"><a href="/"><img style="border:0;width:135px;height:32px" src="/images/toprowlk.gif" alt="lkml.org" /></a></td><td width="32">聽</td><td class="nb"><div><a class="nb" href="/lkml"> [lkml]</a> 聽 <a class="nb" href="/lkml/2005"> [2005]</a> 聽 <a class="nb" href="/lkml/2005/9"> [Sep]</a> 聽 <a class="nb" href="/lkml/2005/9/15"> [15]</a> 聽 <a class="nb" href="/lkml/last100"> [last100]</a> 聽 <a href="/rss.php"><img src="/images/rss-or.gif" border="0" alt="RSS Feed" /></a></div><div>Views: <a href="#" class="nowrap" onclick="setActiveStyleSheet('wrap');return false;">[wrap]</a><a href="#" class="wrap" onclick="setActiveStyleSheet('nowrap');return false;">[no wrap]</a> 聽 <a class="nb" href="/lkml/mheaders/2005/9/15/185" onclick="this.href='/lkml/headers'+'/2005/9/15/185';">[headers]</a>聽 <a href="/lkml/bounce/2005/9/15/185">[forward]</a>聽 </div></td><td width="32">聽</td></tr><tr><td valign="top"><div class="es-jasper-simpleCalendar" baseurl="/lkml/"></div><div class="threadlist">Messages in this thread</div><ul class="threadlist"><li class="root"><a href="/lkml/2005/9/15/185">First message in thread</a></li><li class="origin"><a href="/lkml/2005/9/15/202">WU Fengguang</a><ul><li><a href="/lkml/2005/9/15/202">Paolo Ornati</a><ul><li><a href="/lkml/2005/9/15/207">WU Fengguang</a></li></ul></li></ul></li></ul></td><td width="32" rowspan="2" class="c" valign="top"><img src="/images/icornerl.gif" width="32" height="32" alt="/" /></td><td class="c" rowspan="2" valign="top" style="padding-top: 1em"><table><tr><td><table><tr><td class="lp">Date</td><td class="rp" itemprop="datePublished">Thu, 15 Sep 2005 21:16:51 +0800</td></tr><tr><td class="lp">From</td><td class="rp" itemprop="author">WU Fengguang <></td></tr><tr><td class="lp">Subject</td><td class="rp" itemprop="name">Adaptive read-ahead: benchmarks</td></tr></table></td><td></td></tr></table><pre itemprop="articleBody">I carried out the tests on a DELL PE1750 with 2G memory and a hardware raid5 array built on three 73G SCSI disks. I failed to interpret some of the benchmark results, any comments are greatly appreciated. DEBUG OUTPUT ===================================================================== # cp kernel-image-2.6.13_10.00.Custom_i386.deb /dev/null ----------------------------------------------------------------- the current logic: [17179814.868000] blockable-readahead(ino=83571, ra=0+1) = 1 [17179814.880000] blockable-readahead(ino=83571, ra=1+4) = 4 [17179814.880000] blockable-readahead(ino=83571, ra=5+16) = 16 [17179814.892000] blockable-readahead(ino=83571, ra=21+32) = 32 [17179814.896000] blockable-readahead(ino=83571, ra=53+64) = 64 [17179814.924000] blockable-readahead(ino=83571, ra=117+128) = 128 [17179814.924000] blockable-readahead(ino=83571, ra=245+256) = 256 [17179815.024000] blockable-readahead(ino=83571, ra=501+256) = 256 [17179815.024000] blockable-readahead(ino=83571, ra=757+256) = 256 [17179815.076000] blockable-readahead(ino=83571, ra=1013+256) = 256 [17179815.100000] blockable-readahead(ino=83571, ra=1269+256) = 256 [17179815.184000] blockable-readahead(ino=83571, ra=1525+256) = 256 [17179815.188000] blockable-readahead(ino=83571, ra=1781+256) = 256 [17179815.236000] blockable-readahead(ino=83571, ra=2037+256) = 256 [17179815.272000] blockable-readahead(ino=83571, ra=2293+256) = 256 [17179815.328000] blockable-readahead(ino=83571, ra=2549+256) = 256 [17179815.332000] blockable-readahead(ino=83571, ra=2805+256) = 256 [17179815.368000] blockable-readahead(ino=83571, ra=3061+256) = 256 [17179815.396000] blockable-readahead(ino=83571, ra=3317+256) = 251 [17179815.424000] blockable-readahead(ino=83571, ra=3573+256) = 0 the new logic with readahead-ratio set to 101: [17179673.064000] readahead(ino=83571, index=0-0-1, ra=0+32) = 32 [17179673.084000] readahead(ino=83571, index=32-32-33, ra=32+32) = 32 [17179673.100000] readahead(ino=83571, index=64-64-65, ra=64+64) = 64 [17179673.116000] readahead(ino=83571, index=128-128-129, ra=128+129) = 129 [17179673.144000] readahead(ino=83571, index=257-257-258, ra=257+256) = 256 [17179673.212000] readahead(ino=83571, index=513-513-514, ra=513+256) = 256 [17179673.248000] readahead(ino=83571, index=769-769-770, ra=769+256) = 256 [17179673.288000] readahead(ino=83571, index=1025-1025-1026, ra=1025+256) = 256 [17179673.332000] readahead(ino=83571, index=1281-1281-1282, ra=1281+256) = 256 [17179673.408000] readahead(ino=83571, index=1537-1537-1538, ra=1537+256) = 256 [17179673.440000] readahead(ino=83571, index=1793-1793-1794, ra=1793+256) = 256 [17179673.476000] readahead(ino=83571, index=2049-2049-2050, ra=2049+256) = 256 [17179673.512000] readahead(ino=83571, index=2305-2305-2306, ra=2305+256) = 256 [17179673.576000] readahead(ino=83571, index=2561-2561-2562, ra=2561+256) = 256 [17179673.604000] readahead(ino=83571, index=2817-2817-2818, ra=2817+256) = 256 [17179673.652000] readahead(ino=83571, index=3073-3073-3074, ra=3073+256) = 256 [17179673.704000] readahead(ino=83571, index=3329-3329-3330, ra=3329+256) = 239 OPROFILE STATISTICS ===================================================================== # cat oprofile.sh #!/bin/sh oprofile() { opcontrol --vmlinux=/temp/kernel/linux-2.6.13ra/vmlinux opcontrol --start opcontrol --reset echo $1 > /proc/sys/vm/readahead_ratio dd if=/temp/kernel/hugefile of=/dev/null bs=$bs opreport -l -o oprofile.$1.$bs /temp/kernel/linux-2.6.13ra/vmlinux opcontrol --stop } bs=$1 shift while test -n "$1" do oprofile $1 shift done # ./oprofile.sh 4k 0 100 3932946432 bytes transferred in 80.383702 seconds (48927162 bytes/sec) 3932946432 bytes transferred in 109.835723 seconds (35807534 bytes/sec) # head -n100 oprofile.0.4k CPU: P4 / Xeon with 2 hyper-threads, speed 2388.38 MHz (estimated) Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000 samples % symbol name 34745 14.0697 __copy_to_user_ll 11894 4.8164 ll_rw_block 10362 4.1960 system_call 8669 3.5104 shrink_list 7761 3.1428 radix_tree_delete 7627 3.0885 __find_get_block 6901 2.7945 delay_pmtmr 6474 2.6216 add_to_page_cache 5350 2.1664 dnotify_parent 4868 1.9713 isolate_lru_pages 4768 1.9308 inotify_dentry_parent_queue_event 4453 1.8032 do_generic_mapping_read 4421 1.7902 do_mpage_readpage 4108 1.6635 find_get_page 4047 1.6388 default_idle 4000 1.6198 unlock_buffer 3914 1.5849 __brelse 3850 1.5590 zone_watermark_ok 3777 1.5295 __wake_up_bit 3615 1.4639 __do_page_cache_readahead 3211 1.3003 unlock_page 3095 1.2533 kmap_atomic 3059 1.2387 bad_range 2894 1.1719 __mod_page_state 2665 1.0792 free_pages_bulk 2530 1.0245 __alloc_pages 2385 0.9658 __pagevec_lru_add 2273 0.9204 mpage_end_io_read 2225 0.9010 free_hot_cold_page 2092 0.8471 buffered_rmqueue 1811 0.7333 page_waitqueue 1808 0.7321 radix_tree_lookup 1780 0.7208 __rmqueue 1702 0.6892 find_busiest_group 1672 0.6771 page_referenced 1648 0.6673 mark_page_accessed 1594 0.6455 __read_lock_failed 1560 0.6317 wakeup_kswapd 1557 0.6305 __pagevec_release_nonlru 1464 0.5928 schedule 1449 0.5868 mark_offset_pmtmr 1439 0.5827 radix_tree_insert 1367 0.5536 blk_recount_segments 1306 0.5289 release_pages 1162 0.4705 current_fs_time 1159 0.4693 apic_timer_interrupt 1098 0.4446 mempool_free 1061 0.4296 vfs_read 1045 0.4232 kmem_cache_alloc 1031 0.4175 __write_lock_failed 1019 0.4126 timer_interrupt 931 0.3770 vfs_write 925 0.3746 bit_waitqueue 908 0.3677 mpage_readpages 895 0.3624 find_next_bit 895 0.3624 kmem_cache_free 892 0.3612 __bio_add_page 883 0.3576 irq_entries_start 818 0.3312 sys_write 794 0.3215 sys_read 788 0.3191 restore_nocheck 783 0.3171 __remove_from_page_cache 762 0.3086 __do_IRQ 750 0.3037 __generic_file_aio_read 749 0.3033 page_address 718 0.2907 __getblk 694 0.2810 shrink_cache 686 0.2778 blk_rq_map_sg 654 0.2648 as_completed_request 613 0.2482 shrink_slab 606 0.2454 scheduler_tick 602 0.2438 file_read_actor 589 0.2385 rmqueue_bulk 583 0.2361 generic_file_read 577 0.2337 load_balance 567 0.2296 __make_request 563 0.2280 fget_light 558 0.2260 rw_verify_area 553 0.2239 run_timer_softirq 513 0.2077 radix_tree_preload 513 0.2077 smp_apic_timer_interrupt 495 0.2004 cond_resched 493 0.1996 bio_alloc_bioset 462 0.1871 rebalance_tick 417 0.1689 update_atime 406 0.1644 generic_make_request 389 0.1575 __do_softirq 382 0.1547 cpu_idle 381 0.1543 update_process_times 377 0.1527 prep_new_page 373 0.1510 __end_that_request_first 371 0.1502 balance_pgdat 352 0.1425 as_update_iohist 349 0.1413 tasklet_action 345 0.1397 account_system_time 333 0.1348 __read_page_state 333 0.1348 sched_clock # head -n100 oprofile.100.4k CPU: P4 / Xeon with 2 hyper-threads, speed 2388.38 MHz (estimated) Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000 samples % symbol name 36120 13.7910 __copy_to_user_ll 12537 4.7868 ll_rw_block 10416 3.9770 system_call 8790 3.3561 shrink_list 8147 3.1106 radix_tree_delete 7833 2.9907 __find_get_block 7731 2.9518 delay_pmtmr 6651 2.5394 add_to_page_cache 5346 2.0412 dnotify_parent 5174 1.9755 default_idle 5174 1.9755 isolate_lru_pages 4966 1.8961 inotify_dentry_parent_queue_event 4626 1.7663 do_generic_mapping_read 4418 1.6868 do_mpage_readpage 4054 1.5479 __brelse 4033 1.5398 __wake_up_bit 4012 1.5318 unlock_buffer 3906 1.4914 find_get_page 3859 1.4734 zone_watermark_ok 3712 1.4173 __do_page_cache_readahead 3418 1.3050 unlock_page 3194 1.2195 bad_range 3109 1.1871 kmap_atomic 3029 1.1565 __mod_page_state 2603 0.9939 __alloc_pages 2594 0.9904 free_pages_bulk 2356 0.8995 __pagevec_lru_add 2309 0.8816 find_busiest_group 2227 0.8503 free_hot_cold_page 2126 0.8117 schedule 2078 0.7934 mpage_end_io_read 2030 0.7751 buffered_rmqueue 2015 0.7694 mark_offset_pmtmr 1943 0.7419 radix_tree_lookup 1904 0.7270 page_waitqueue 1898 0.7247 __rmqueue 1774 0.6773 page_referenced 1720 0.6567 mark_page_accessed 1672 0.6384 __read_lock_failed 1646 0.6285 __pagevec_release_nonlru 1614 0.6162 wakeup_kswapd 1511 0.5769 apic_timer_interrupt 1471 0.5616 radix_tree_insert 1452 0.5544 blk_recount_segments 1437 0.5487 release_pages 1320 0.5040 timer_interrupt 1247 0.4761 current_fs_time 1149 0.4387 vfs_read 1133 0.4326 mempool_free 1129 0.4311 find_next_bit 1105 0.4219 kmem_cache_alloc 1048 0.4001 __write_lock_failed 1023 0.3906 irq_entries_start 929 0.3547 vfs_write 902 0.3444 bit_waitqueue 887 0.3387 __generic_file_aio_read 878 0.3352 kmem_cache_free 865 0.3303 __bio_add_page 861 0.3287 load_balance 853 0.3257 __do_IRQ 843 0.3219 mpage_readpages 840 0.3207 page_address 839 0.3203 __remove_from_page_cache 822 0.3138 restore_nocheck 810 0.3093 sys_read 787 0.3005 sys_write 776 0.2963 __getblk 749 0.2860 scheduler_tick 726 0.2772 shrink_cache 707 0.2699 run_timer_softirq 656 0.2505 blk_rq_map_sg 651 0.2486 as_completed_request 651 0.2486 file_read_actor 642 0.2451 smp_apic_timer_interrupt 610 0.2329 rw_verify_area 604 0.2306 shrink_slab 600 0.2291 rebalance_tick 598 0.2283 rmqueue_bulk 590 0.2253 generic_file_read 570 0.2176 fget_light 558 0.2131 __make_request 524 0.2001 update_process_times 523 0.1997 bio_alloc_bioset 522 0.1993 cond_resched 506 0.1932 radix_tree_preload 502 0.1917 __do_softirq 482 0.1840 cpu_idle 454 0.1733 sched_clock 437 0.1669 update_atime 430 0.1642 account_system_time 425 0.1623 generic_make_request 412 0.1573 __switch_to 399 0.1523 tasklet_action 396 0.1512 rt_run_flush 395 0.1508 try_to_wake_up 390 0.1489 __read_page_state 369 0.1409 balance_pgdat additional two lines: 324 0.1237 page_cache_readahead_adaptive 46 0.0176 count_sequential_pages Summary: 1. The real time of dd is 80.383702 to 109.835723, or 1:1.37. The current logic has an 'ahead window' and always issues readaheads ahead of time, which effectively prevents reads to stall from time to time. The new logic simply issues readaheads at times of immediate need. So the difference is quite reasonable. 2. The new logic shows 5% or so overhead, though the direct overhead of the two functions is only 2%. Where is the remaining 3%? Locking contentions somewhere? SEQUENTIAL READ PATTERNS ===================================================================== # cat test_ra.sh #!/bin/zsh blockdev --setra 256 /dev/sda echo deadline > /sys/block/sda/queue/scheduler TIMEFMT="%E real %S system %U user %w+%c cs %J" FILE=hugefile bs=$1 shift while test -n "$1" do echo $1 > /proc/sys/vm/readahead_ratio cp $FILE /dev/null echo "readahead_ratio = $1" time dd if=$FILE of=/dev/null bs=$bs 2>/dev/null time grep -r 'asdfghjkl;' linux-2.6.13 & time dd if=$FILE of=/dev/null bs=$bs 2>/dev/null & time diff -r linux-2.6.13 linux-2.6.13ra >/dev/null & sleep 20 while {pidof dd diff grep > /dev/null}; do sleep 3 done shift done # ./test_ra.sh 4k 0 100 readahead_ratio = 0 79.75s real 8.88s system 0.43s user 13927+10 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 142.75s real 1.37s system 24.16s user 13724+42 cs grep -r 'asdfghjkl;' linux-2.6.13 167.09s real 9.47s system 0.50s user 25065+30 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 173.99s real 3.70s system 1.48s user 31148+10 cs diff -r linux-2.6.13 linux-2.6.13ra > /dev/null readahead_ratio = 100 107.51s real 8.58s system 0.48s user 28065+8 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 149.86s real 1.60s system 23.57s user 14372+42 cs grep -r 'asdfghjkl;' linux-2.6.13 178.63s real 9.52s system 0.51s user 32047+34 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 184.56s real 3.87s system 1.34s user 32399+6 cs diff -r linux-2.6.13 linux-2.6.13ra > /dev/null Summary: 1. The blockdev command takes no effect at all -- the readahead-max is still 1M. 2. In single stream, the new logic seems to get lower system time, doesn't it conflict with that of oprofile? And context switches are more than doubled, but why? 3. In parallel streams, the new logic gets more system time and lower user time, context switches are roughly the same. The 'ahead window' magic should work only for large files, though the new logic losed again in small files. Maybe it's the 3 radix tree lookups that show up in small reads? To find things out, I add a call to lock_page() at the end of __do_page_cache_readahead(), and the code can be enabled with some readahead_ratio values(such as 102). The command below runs the test with the page lock: # ./test_ra.sh 4k 102 readahead_ratio = 102 108.66s real 9.43s system 0.48s user 10235+132 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 192.52s real 1.87s system 23.86s user 19073+321 cs grep -r 'asdfghjkl;' linux-2.6.13 201.40s real 9.99s system 0.46s user 17490+141 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 209.59s real 4.37s system 1.55s user 36987+68 cs diff -r linux-2.6.13 linux-2.6.13ra > /dev/null It shows that context switches are effectively cut down in dd, though system times are even higher. MORE DATA ===================================================================== Some more tests with 32k block size: # ./test_ra.sh 32k 0 100 102 readahead_ratio = 0 80.05s real 7.98s system 0.07s user 14044+117 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 148.02s real 1.38s system 24.45s user 13532+310 cs grep -r 'asdfghjkl;' linux-2.6.13 178.84s real 8.66s system 0.08s user 26165+130 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 180.80s real 4.01s system 1.54s user 32994+67 cs diff -r linux-2.6.13 linux-2.6.13ra > /dev/null readahead_ratio = 100 108.13s real 7.92s system 0.05s user 28877+97 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 157.50s real 1.50s system 22.35s user 14842+291 cs grep -r 'asdfghjkl;' linux-2.6.13 185.94s real 8.81s system 0.09s user 34166+117 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 190.27s real 3.90s system 1.60s user 35728+66 cs diff -r linux-2.6.13 linux-2.6.13ra > /dev/null readahead_ratio = 102 112.04s real 9.22s system 0.48s user 10483+136 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 190.23s real 1.74s system 21.76s user 19097+279 cs grep -r 'asdfghjkl;' linux-2.6.13 199.14s real 10.10s system 0.56s user 17904+179 cs dd if=$FILE of=/dev/null bs=$bs 2> /dev/null 207.10s real 4.20s system 1.43s user 38820+63 cs diff -r linux-2.6.13 linux-2.6.13ra > /dev/null More oprofile results: # head -n20 oprofile.0.4k PU: P4 / Xeon with 2 hyper-threads, speed 2388.41 MHz (estimated) Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000 samples % symbol name 34763 14.0479 __copy_to_user_ll 15171 6.1307 ll_rw_block 10795 4.3623 system_call 10254 4.1437 shrink_list 9199 3.7174 __find_get_block 7818 3.1593 delay_pmtmr 6480 2.6186 add_to_page_cache 5541 2.2391 radix_tree_delete 5478 2.2137 isolate_lru_pages 5474 2.2121 dnotify_parent 5141 2.0775 __brelse 5014 2.0262 inotify_dentry_parent_queue_event 4838 1.9551 unlock_buffer 4790 1.9357 find_get_page 4618 1.8662 do_mpage_readpage 4390 1.7740 do_generic_mapping_read 3989 1.6120 default_idle # head -n20 oprofile.102.4k CPU: P4 / Xeon with 2 hyper-threads, speed 2388.41 MHz (estimated) Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000 samples % symbol name 34954 14.0548 __copy_to_user_ll 14888 5.9864 ll_rw_block 10895 4.3808 shrink_list 10398 4.1810 system_call 9109 3.6627 __find_get_block 8003 3.2180 delay_pmtmr 6746 2.7125 add_to_page_cache 5752 2.3128 radix_tree_delete 5644 2.2694 isolate_lru_pages 5354 2.1528 dnotify_parent 5004 2.0121 __brelse 4952 1.9912 default_idle 4900 1.9703 find_get_page 4845 1.9481 inotify_dentry_parent_queue_event 4711 1.8943 unlock_buffer 4404 1.7708 do_generic_mapping_read 4135 1.6627 do_mpage_readpage # head -n20 oprofile.0.32k CPU: P4 / Xeon with 2 hyper-threads, speed 2388.41 MHz (estimated) Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000 samples % symbol name 36906 16.4281 __copy_to_user_ll 15199 6.7656 ll_rw_block 10248 4.5617 shrink_list 9276 4.1291 __find_get_block 7811 3.4769 delay_pmtmr 6706 2.9851 add_to_page_cache 6028 2.6833 isolate_lru_pages 5855 2.6063 radix_tree_delete 5577 2.4825 find_get_page 4959 2.2074 __brelse 4931 2.1950 unlock_buffer 4189 1.8647 do_mpage_readpage 4025 1.7917 default_idle 3869 1.7222 mpage_end_io_read 3809 1.6955 __do_page_cache_readahead 3069 1.3661 kmap_atomic 2814 1.2526 __read_lock_failed # head -n20 oprofile.100.32k CPU: P4 / Xeon with 2 hyper-threads, speed 2388.41 MHz (estimated) Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000 samples % symbol name 37118 15.8645 __copy_to_user_ll 15602 6.6684 ll_rw_block 10664 4.5579 shrink_list 9487 4.0548 __find_get_block 8366 3.5757 delay_pmtmr 6902 2.9500 add_to_page_cache 6192 2.6465 isolate_lru_pages 5989 2.5597 radix_tree_delete 5164 2.2071 __brelse 5060 2.1627 unlock_buffer 4962 2.1208 default_idle 4668 1.9951 find_get_page 4381 1.8725 do_mpage_readpage 3957 1.6912 __do_page_cache_readahead 3223 1.3775 kmap_atomic 3185 1.3613 mpage_end_io_read 3080 1.3164 __wake_up_bit # head -n20 oprofile.102.32k CPU: P4 / Xeon with 2 hyper-threads, speed 2388.41 MHz (estimated) Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped) with a unit mask of 0x01 (mandatory) count 100000 samples % symbol name 34634 15.8598 __copy_to_user_ll 14628 6.6985 ll_rw_block 10239 4.6887 shrink_list 8721 3.9936 __find_get_block 7880 3.6085 delay_pmtmr 6424 2.9417 add_to_page_cache 5654 2.5891 isolate_lru_pages 5418 2.4810 radix_tree_delete 5104 2.3373 find_get_page 4860 2.2255 default_idle 4821 2.2077 __brelse 4765 2.1820 unlock_buffer 4008 1.8354 do_mpage_readpage 3322 1.5212 __do_page_cache_readahead 3114 1.4260 __read_lock_failed 2959 1.3550 kmap_atomic 2713 1.2424 __wake_up_bit LARGE READ SIZE ===================================================================== There is an early (broken) version that issues the next readahead when only 1/4 of the previous readahead pages are left. This behaves like the current logic, and the results are exciting. But I think it is not sane to search through the page cache too much. The default kernel on my PC with 128K readahead-max: ==================================================================== readahead_ratio = 0 22387+1 records in 22387+1 records out 733589504 bytes transferred in 25.293262 seconds (29003357 bytes/sec) 0.01s user 1.56s system 6% cpu 25.310 total 22326+1 records in 22326+1 records out 731596800 bytes transferred in 103.776015 seconds (7049768 bytes/sec) 0.01s user 1.54s system 1% cpu 1:43.85 total 0.38s user 1.50s system 1% cpu 2:09.72 total -------------------------------------------------------------------- An early version of the new logic with 2M readahead-max: ==================================================================== readahead_ratio = 90 22387+1 records in 22387+1 records out 733589504 bytes transferred in 21.265200 seconds (34497183 bytes/sec) 0.01s user 1.56s system 7% cpu 21.334 total 22326+1 records in 22326+1 records out 731596800 bytes transferred in 42.916377 seconds (17047031 bytes/sec) 0.02s user 1.51s system 3% cpu 43.126 total 0.37s user 1.44s system 2% cpu 1:08.89 total -------------------------------------------------------------------- It effectively shows the advantage of large readahead sizes ;) -- WU Fengguang Dept. of Automation University of Science and Technology of China Hefei, Anhui - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at <a href="http://vger.kernel.org/majordomo-info.html">http://vger.kernel.org/majordomo-info.html</a> Please read the FAQ at <a href="http://www.tux.org/lkml/">http://www.tux.org/lkml/</a> </pre></td><td width="32" rowspan="2" class="c" valign="top"><img src="/images/icornerr.gif" width="32" height="32" alt="\" /></td></tr><tr><td align="right" valign="bottom"> 聽 </td></tr><tr><td align="right" valign="bottom">聽</td><td class="c" valign="bottom" style="padding-bottom: 0px"><img src="/images/bcornerl.gif" width="32" height="32" alt="\" /></td><td class="c">聽</td><td class="c" valign="bottom" style="padding-bottom: 0px"><img src="/images/bcornerr.gif" width="32" height="32" alt="/" /></td></tr><tr><td align="right" valign="top" colspan="2"> 聽 </td><td class="lm">Last update: 2005-09-15 15:16 聽聽 [from the cache] 漏2003-2020 <a href="http://blog.jasper.es/">Jasper Spaans</a>|hosted at <a href="https://www.digitalocean.com/?refcode=9a8e99d24cf9">Digital Ocean</a> and my Meterkast|<a href="http://blog.jasper.es/categories.html#lkml-ref">Read the blog</a></td><td>聽</td></tr></table><script language="javascript" src="/js/styleswitcher.js" type="text/javascript"></script></body></html>