-What's new in the Linux kernel - DebConf 2013
+What's new in the Linux kernel - DebConf 2014
@@ -39,7 +39,7 @@
@@ -50,6 +50,7 @@
What's new in the Linux kernel
+
and what's missing in Debian
Ben Hutchings
@@ -58,23 +59,21 @@
Professional software engineer by day, Debian developer by night
+ (or sometimes the other way round)
Regular Linux contributor in both roles since 2008
-
-
- Maintaining a net driver in my day job, plus core networking
- and PCI code as necessary
-
-
- Debian kernel team member, now doing most of the unstable
- maintenance aside from ports
-
-
- Maintaining Linux 3.2.y stable update series on
- kernel.org
-
-
+
+
+ Working on various drivers and kernel code in my day job
+
+
+ Debian kernel team member, now doing most of the unstable
+ maintenance aside from ports
+
+
+ Maintaining Linux 3.2.y stable update series on
+ kernel.org
@@ -85,10 +84,15 @@
Linux is released about 5 times a year (plus stable updates
every week or two)
+
+
+ ...though some features aren't ready to use when they firat
+ appear in a release
+
+
- For 'wheezy' we chose to freeze with Linux 3.2, which was
- getting pretty old by the time of release
+ Since my talk last year, Linus has made 6 releases (3.11-3.16)
Good news: we have lots of new kernel features in testing/unstable
@@ -99,6 +103,156 @@
+
+
Recap of last year's features (1)
+
+
+ Team device driver: userland package (libteam) was uploaded in
+ October
+
+
+ Transcendent memory: frontswap, zswap and Xen tmem will be
+ enabled in next kernel upload
+
+
+ New KMS drivers: should all work with current Xorg drivers
+
+
+ Module signing: still not enabled, but probably will be if we
+ do Secure Boot
+
+
+
+
+
+
Recap of last year's features (2)
+
+
+ More support for discard: still not enabled at install time
+ (#690977)
+
+
+ More support for containers: XFS was fixed, and user namespaces
+ have been enabled
+
+
+ bcache: userland package (bcache-tools) still not quite ready
+ (#708132)
+
+
+ ARMv7 multiplatform: d-i works on some platforms but
+ I'm still not sure which. Some progress on GPU drivers, but not
+ in Debian yet.
+
+
+
+
+
+
Unnamed temporary files [3.11]
+
+
+ Open directory with option O_TMPFILE to create an
+ unnamed temporary file on that filesystem
+
+
+ As with tmpfile(), the file disppears on
+ last close()
+
+
+ File can be linked into the filesystem using
+ linkat(..., AT_EMPTY_PATH), allowing for 'atomic'
+ creation of file with complete contents and metadata
+
+
+ Not supported on all filesystem types, so you will usually need
+ a fallback
+
+
+
+
+
+
Lustre filesystem [3.12]
+
+
+ A distributed filesystem, popular for cluster computing
+ applications
+
+
+ Developed out-of-tree since 1999, but now added to Linux staging
+ directory
+
+
+ Was included in squeeze but dropped from wheezy as it didn't
+ support Linux 3.2
+
+
+ Userland is now missing from Debian
+
+
+
+
+
+
Network busy-polling [3.11] (1)
+
A conventional network request/response process looks like:
+
+
+
+ Task calls send(); network stack constructs a
+ packet; driver adds it to hardware Tx queue
+
+
+ Task calls poll() or recv(), which blocks;
+ kernel puts it to sleep and possibly idles the CPU
+
+
+ Network adapter receives response and generates IRQ, waking
+ up CPU
+
+
+ Driver's IRQ handler schedules polling of the hardware Rx
+ queue (NAPI)
+
+
+ Kernel runs the driver's NAPI poll function, which passes
+ the response packet into the network stack
+
+
+ Network stack decodes packet headers and adds packet to
+ the task's socket
+
+
+ Network stack wakes up sleeping task; scheduler switches
+ to it and the socket call returns
+
+
+
+
+
+
+
Network busy-polling [3.11] (2)
+
+
+ If driver supports busy-polling, it tags each packet with
+ the receiving NAPI context, and kernel tags sockets
+
+
+ When busy-polling is enabled, poll()
+ and recv() call the driver's busy poll function to
+ check for packets synchronously (up to some time limit)
+
+
+ If the response usually arrives quickly, this reduces overall
+ request/response latency as there are no context switches and
+ power transitions
+
+
+ Time limit set by sysctl (net.busy_poll,
+ net.busy_read) or socket option (SOL_SOCKET,
+ SO_BUSY_POLL); requires tuning
+