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Linux Multi-Queue Block IO Queueing Mechanism (blk-mq) Details - Thomas-Krenn-Wiki-en
Blk-mq integrates seamlessly into the Linux storage stack. It provides basic functions to device drivers for mapping I/O enquiries to multiple queues. The tasks are distributed across multiple threads and therefore to multiple CPU cores (per-core software queues). Blk-mq compatible drivers inform blk-mq how many parallel hardware queues a device supports (number of submission queues as part of the
Flushing out pdflush [LWN.net]
April 1, 2009 This article was contributed by Goldwyn Rodrigues The kernel page cache contains in-memory copies of data blocks belonging to files kept in persistent storage. Pages which are written to by a processor, but not yet written to disk, are accumulated in cache and are known as "dirty" pages. The amount of dirty memory is listed in /proc/meminfo. Pages in the cache are flushed to disk aft
iostat: (r/s + w/s) * svctm = %util on Linux
iostat -x is very useful to check disk i/o activities. Sometimes it is said that "check %util is less than 100%" or "check svctm is less than 50ms", but please do not fully trust these numbers. For example, the following two cases (DBT-2 load on MySQL) used same disks (two HDD disks, RAID1) and reached almost 100% util, but performance numbers were very different (no.2 was about twice as fast as n
iostat ã®è¦‹æ–¹ - ablog
出力例 $ iostat -x 30 avg-cpu: %user %nice %system %iowait %steal %idle 0.87 0.01 2.53 0.49 0.00 96.11 Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util sda 0.05 16.03 0.36 13.74 5.77 238.22 17.31 0.15 10.39 0.98 1.38 sda1 0.00 0.00 0.00 0.00 0.00 0.00 15.53 0.00 12.81 11.47 0.00 sda2 0.05 16.03 0.36 13.74 5.77 238.22 17.31 0.15 10.39 0.98 1.38 avg-cpu: %user %nice %syst
iostat await svctm 㮠見ã‹ãŸã€è€ƒãˆæ–¹
4. 4  下記ã¯iostat -x ã®ãƒã‚°ã®ã‚µãƒ³ãƒ—ル iostat -x 1 ： avg-cpu: %user %nice %system %iowait %steal %idle 0.76 0.00 0.51 1.52 0.00 97.22 Device: rrqm/s … rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util sda 0.00 … 2000.00 88.00 208.80 0.14 13.70 8.00 8.00 sdb 0.00 … 0.00 24.00 8.00 0.09 31.33 21.67 6.50 avg-cpu: %user %nice %system %iowait %steal %idle 0.76 0.00 0.51 0.25 0.00 98.48 Device: rrqm/s … rsec/s ws
Fsync Performance on Storage Devices
All of Percona’s open-source software products, in one place, to download as much or as little as you need.
ãƒãƒƒãƒ•ã‚¡ã‚ャッシュã¨AIO（1）
プãƒã‚»ã‚¹ãŒãƒ–ãƒãƒƒã‚¯ã™ã‚‹è¦å› ã®ä¸€ã¤ã«ãƒ•ã‚¡ã‚¤ãƒ«I/OãŒã‚ã‚Šã¾ã™ã€‚ã“れをåŒæœŸI/Oã¨è¨€ã„ã¾ã™ãŒã€POSIXã§ã¯AIO（éžåŒæœŸ I/Oã€Asynchronous I/O）も定義ã—ã¦ãŠã‚Šã€I/Oä¸ã§ã‚‚プãƒã‚»ã‚¹ãŒãƒ–ãƒãƒƒã‚¯ã›ãšä»–ã®å‡¦ç†ã‚’進ã‚られるよã†ã«ãªã‚Šã¾ã™ã€‚ 本記事ã§ã¯ãƒãƒƒãƒ•ã‚¡ã‚ャッシュã‹ã‚‰ãƒ•ã‚¡ã‚¤ãƒ« I/Oを解説ã—ã€Linuxã®io_submit(2)を用ã„ãŸPOSIXæº–æ‹ ã®AIOライブラリを試作ã—ã¦ã¿ã¾ã™ã€‚ ファイルI/Oã¨ãƒãƒƒãƒ•ã‚¡ã‚ャッシュ io_submit(2)ã§ã¯Direct I/Oを用ã„ã¾ã™ãŒã€ãƒ©ã‚¤ãƒ–ラリã®è©¦ä½œã¸é€²ã‚€å‰ã«ã¾ãšãƒ•ã‚¡ã‚¤ãƒ«I/Oã®ãƒãƒƒãƒ•ã‚¡ï¼ˆãƒãƒƒãƒ•ã‚¡ã‚ャッシュ）ã«ã¤ã„ã¦æ•´ç†ã—ã¾ã™ã€‚実ã¯å˜ã«ãƒãƒƒãƒ•ã‚¡ã¨è¨€ã£ã¦ã—ã¾ã†ã¨èª¤è§£ã•ã‚Œã‚‹å ´é¢ãŒå¤šãã‚ã‚Šã€ä¾‹ãˆã°ãƒ—ãƒã‚°ãƒ©ãƒŸãƒ³ã‚°å…¥é–€ä¸€èˆ¬ã¨ã—ã¦ãƒ•ã‚¡ã‚¤ãƒ«I/Oã‚’å–り上ã’ã‚‹éš›ã«ã¯ã€ CPUã®å‹•ä½œã¯é€Ÿã„。ディスクã®å‹•ä½œã¯é…ã„。 両者ã®é–“ã«é€Ÿåº¦å·®ã‚’ç·©å’Œã™ã‚‹ç·©è¡
Efficient File Copying On Linux
In response to my last post about dd, a friend of mine noticed that GNU cp always uses a 128 KB buffer size when copying a regular file; this is also the buffer size used by GNU cat. If you use strace to watch what happens when copying a file, you should see a lot of 128 KB read/write sequences: $ strace -s 8 -xx cp /dev/urandom /dev/null ... read(3, "\x61\xca\xf8\xff\x1a\xd6\x83\x8b"..., 131072)
Why buffered writes are sometimes stalled
Many people think buffered write (write()/pwrite()) is fast because it does not do disk access. But this is not always true. Buffered write sometimes does disk access by itself, or waits for some disk accesses by other threads. Here are three common cases where write() takes longer time (== causing stalls). 1. Read Modify Write Suppose the following logic. Opening aaa.dat without O_DIRECT/O_SYNC,
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ext4: using external journal to optimise performance
OS Configurations for Better Hadoop Performance
Dynamic writeback throttling [LWN.net]
How I Use iostat and vmstat for Performance Analysis - Yubin Xia
Better Linux Disk Caching & Performance with vm.dirty_ratio
New community features for Google Chat and an update on Currents
databasss – Medium
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