The kernel report. Jonathan Corbet LWN.net

Transcription

1 The kernel report Jonathan Corbet LWN.net

2 What we'll talk about 1) Process - releases and such (how we got to where we are) 2) Features and futures (Cool stuff and what it's good for)

3 Cadence The cycle began February 25, 2010 Since then: Four releases have been made (another almost ready) 49,079 changesets have been merged...from 2,826 developers, 326 employers 1.3 million lines of code have been added

4 The process is working smoothly

5 Who supports this work Volunteers Red Hat unknown Intel Novell IBM Nokia Consultants Texas Inst. Oracle AMD 17.6% 11.7% 7.7% 6.7% 4.8% 3.7% 2.3% 2.2% 2.2% 1.7% 1.6% Samsung academics Fujitsu Renesas Tech. Pengutronix Google Broadcom Atheros Analog Devices Wolfson Micro New Dream Net 1.5% 1.4% 1.4% 1.4% 1.3% 1.2% 1.1% 1.1% 1.1% 1.0% 1.0%

6 The version Unknown Red Hat IBM Novell Linux Found. Hobbyists Intel Oracle Google 27% 14% 8% 7% 5% 5% 4% 2% 2% SGI MIPS Tech. HP Consultants Nokia Astaro MontaVista Linux Networx Qlogic 2% 1% 1% 1% 1% 1% 1% 1% 1%

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8 Who supports this work Volunteers Red Hat unknown Intel Novell IBM Nokia Consultants Texas Inst. Oracle AMD 17.6% 11.7% 7.7% 6.7% 4.8% 3.7% 2.3% 2.2% 2.2% 1.7% 1.6% Samsung academics Fujitsu Renesas Tech. Pengutronix Google Broadcom Atheros Analog Devices Wolfson Micro New Dream Net 1.5% 1.4% 1.4% 1.4% 1.3% 1.2% 1.1% 1.1% 1.1% 1.0% 1.0%

9 May 15, 2010 (9,443 changes, 1,151 developers) Asynchronous suspend/resume perf lock, perf Python scripting support LogFS Ceph distributed filesystem

10 Aug. 1, 2010 (9,801 changes, 1,188 developers) perf kvm Receive packet/flow steering Memory compaction Idle pattern detection RAMoops Btrfs direct I/O support

11 Oct. 20, 2010 (9,501 changes, 1,176 developers) AppArmor security module Wakeup counts LIRC infrared drivers New OOM killer fanotify Concurrency-managed workqueues

12 Jan 4, 2011 (11,446 changes, 1,276 developers) VFS scalability work (inode_lock removal) GFS2 is no longer experimental Block I/O bandwidth controller PPTP support Basic pnfs support Hugepage migration Wakeup sources Block layer barrier work

13 Mar.??, 2011 (8,888 changes, 1,111 developers) (so far) Per-session group scheduling Dcache scalability work Transmit packet steering Batch discard You are here Transparent hugepages Multitouch panel support SCSI target subsystem Btrfs: read-only snapshots and LZO compression

14 Stable updates Mainline release is not the end of the story Stable/longterm updates for: Serious bug fixes Simple hardware support (PCI IDs) Occasional backports

15 Currently-maintained stable kernels Long term, deep freeze mode Base of a number of enterprise distributions Embedded flag version Recent mainline releases

16 Currently-maintained stable kernels Long term, deep freeze mode Base of a number of enterprise distributions Embedded flag version Recent mainline releases

17 Currently-maintained stable kernels Long term, deep freeze mode Base of a number of enterprise distributions Embedded flag version Recent mainline releases

18 What's coming?

19 (Merge window is still open) O_PATH opens Open by file handle CLOCK_BOOTTIME...

20 A new version numbering scheme? No.

21 A new version numbering scheme? No. (At least, not until we hit )

22 Hardware support and vendor participation

23 Good news: Broadcom releases an open driver Qualcomm joins the Linux Foundation Ralink starts submitting patches Embedded flag kernel

24 On the other hand: Embedded graphics remains a problem GPL compliance is spotty

25 Power management CPU power management works very well Now working on memory, peripherals

26 Power management Android code still not merged. We do have an alternative: Wakeup sources (2.6.36) Wakeup counters (2.6.37) Currently unused

27 Power domains Server or desktop PM is relatively simple Newer systems less so

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29 Dealing with complexity Power domains Map power relationships on each system Used to make power management decisions (maybe) Media controller subsystem Handle connections between media processors (probably)

30 Other things to watch for ARM PAE support >4GB in your pocket maybe Device tree support...over time Vast numbers of new drivers...as always

31 Solid-state devices

32 Solid-state devices

33 SSD challenges Optimizing I/O patterns Transfer sizes and alignment Block I/O subsystem scalability 100 I/O operations/second -> 100,000+ IOPS Communication with the device TRIM/DISCARD operations

34 What will we do with that much fast memory?

35 SCSI targets Linux as a SCSI device Useful for storage arrays and such Replaces STGT Two choices: LIO (now in-tree) SCST (out-of-tree)

36 Dentry scalability A directory entry (dentry) represents a name in the filesystem.

37 The dentry scalability patches Remove dcache_lock Use RCU for walking the dentry tree Result: lockless file name lookup

38 Filesystems Ext4 Ready for production use Ongoing scalability work Occasional bug fixes Ext2/ext3 code removal?

39 Filesystems Btrfs Almost there Needs a filesystem checker Remaining features Deduplication RAID 4/5 support Beginning deployment Default MeeGo filesystem Default for Fedora 16?

40 Filesystems Others yaffs2 Fast embedded filesystem ? xfs Continued evolution GFS2 no longer experimental Merge with OCFS2?

41 Transparent huge pages Linux uses 4096-byte pages (most arch's)

42 Transparent huge pages The processor can deal with larger sizes 2MB is common

43 Virtual address translations Address translation is complicated

44 The translation lookaside buffer Caches address mappings -> Avoids that whole lookup process The TLB tends to be small On this laptop: 128 instruction, 256 data One 2M huge page saves 511 TLB entries! (If all internal pages are used) Thus: huge pages make the system go faster

45 Transparent huge pages Linux has had hugetlbfs for years Fiddly, administration-heavy mechanism THP makes huge pages just happen Not as fast as hugetlbfs But it works for everybody Merged for

46 Other memory management issues Writeback One of our biggest performance problems Hybrid memory techniques KSM Transcendent memory...

47 Control groups A means for grouping related processes

48 Control groups Are hierarchical Groups can contain other groups Are inherited Children stay in their parent's group Are associated with controllers Apply some policy to contained processes

49 Control groups Are hierarchical Groups can contain other groups Are inherited Children stay in their parent's group Are associated with controllers Apply some policy to contained processes Are old news...merged in

50 Group CPU scheduling

51 Per-session group scheduling Group scheduling is old...but nobody was using it Per-session group scheduling Makes it all just work Interactivity improvements result

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55 Other control group stuff Expanded group scheduling Systemd/gnome-session integration Nice separation of tasks Bandwidth control Memory controller More focused reclaim Block I/O controller Hierarchical group I/O scheduling Asynchronous I/O control...

56 Deadline scheduling Of interest to real time, media communities Chilly reception at the 2010 kernel summit Needs better use cases Work continues We'll have it someday

57 Realtime Preemption patch set We'll have that someday too!

58 Networking Expand initial congestion window DFS compliance Ongoing issues: IPv6 Bufferbloat Scalability Photo: Arenamontanus

59 Security Stackable modules Hardening An area of increased focus Photo: CarbonNYC User namespaces Unprivileged container creation

60 Tracing and visibility Continued ftrace and perf work Emphasis on usability and unification Addition of tracepoints Improved user-space tracing/debugging Someday Still outside: SystemTap LTTng

61 Things not discussed Thousands of bug fixes Virtualization Additional architectures Documentation RAS improvements CPU isolation Interrupt layer rework Clock enhancements MM preemptability Regression tracking BKL removal...

62 Questions?