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1.8. Easy local kernel configuration
Most people uses the kernel shipped by distros - and that's good. But some people like to compile their own kernels from kernel.org, or maybe they like following the Linux development and want to try it. Configuring your own kernel, however, has become a very difficult and tedious task - there're too many options, and some times userspace software will stop working if you don't enable some key option. You can use a standard distro .config file, but it takes too many time to compile all the options it enables.

To make easier the process of configuration, a new build target has been added: make localmodconfig. It runs "lsmod" to find all the modules loaded on the current running system. It will read all the Makefiles to map which CONFIG enables a module. It will read the Kconfig files to find the dependencies and selects that may be needed to support a CONFIG. Finally, it reads the .config file and removes any module "=m" that is not needed to enable the currently loaded modules. With this tool, you can strip a distro .config of all the unuseful drivers that are not needed in our machine, and it will take much less time to build the kernel. There's an additional "make localyesconfig" target, in case you don't want to use modules and/or initrds.

1.5. CFQ low latency mode
Recommended LWN commentary from Jens Axboe

In this release, the CFQ IO scheduler (the one used by default) gets a new feature that greatly helps to reduce the impact that a writer can have on the system interactiveness. The end result is that the desktop experience should be less impacted by background IO activity, but it can cause noticeable performance issues, so people who only cares about throughput (ie, servers) can try to turn it off echoing 0 to /sys/class/block/<device name>/queue/iosched/low_latency. It's worth mentioning that the 'low_latency' setting defaults to on.

Code: (commit), (commit)

1.8. Easy local kernel configuration

jimmy_page_89 ha scritto:e il modo per non metterli come moduli, ma statici sarebbe make localesconfig? (da quello che leggo, ma chiedo per conferma)

Paoletta ha scritto:

jimmy_page_89 ha scritto:e il modo per non metterli come moduli, ma statici sarebbe make localesconfig? (da quello che leggo, ma chiedo per conferma)

yes...davvero comoda la cosa (anche se bisogna comunque collegare tutto quello che non utilizziamo sempre)

DarthSteve ha scritto:Allora... ho compilato il kernel... e provato le nuove -features-
e sembra, per ora, funzionare come specificato ...
ma ho un 'piccolo' effetto collaterale che e; il seguente:

Con il comando 'halt' or 'shutdown -h now' (da console)
il computer e il monitor rimangono accesi !?!

- Cosa ho sbagliato ?
- TIA!

Bart ha scritto:Fantastica questa feature. Grazie per la segnalazione.
Non mi è molto chiaro il punto "1.5. CFQ low latency mode" evidenziato da Toni.

What the 'low_latency' knob does
Posted Oct 8, 2009 7:11 UTC (Thu) by axboe (subscriber, #904)
Parent article: The CFQ "low latency" mode

The description of the 'low_latency' mode isn't very accurate unfortunately, perhaps Jon didn't have his coffee before reading over it :-). Let me attempt to rectify that.

The low_latency knob doesn't impact delays or merging, one of the key aspects to getting low latency for a series of operations (like starting your firefox while other IO is happening) is actually making sure we get the delays right. If we take the classic case of reader vs writer, the writer dirty speed will greatly outnumber the writeback speed. So we always have tons of dirty pages waiting to be written. The normal reader, however, does dependent reads that are serialized by each other. When one read finishes, another will be issued by the reader very shortly. Achieving good throughput and latency for the reader in CFQ is accomplished by briefly waiting for another IO when one has completed. In CFQ, this is called idling.

The two primary changes in behaviour for CFQ in -rc3 is letting seeky IO also idle, even if the hardware does command queuing (which most does these days) and limiting the damage that the async IO can do while sync IO is also happening. With the 'low_latency' knob switched to on, CFQ will only slowly build up a queue depth of async writes. This greatly helps reduce the impact that a writer will have on the system interactiveness, since when we miss a sync idle window only slightly, the amount of async writeback sent to the device will be limited by the time since that last sync IO.

The end result is that the desktop experience should be less impacted by background IO activity. It's also worth mentioning that the 'low_latency' setting defaults to on.

jimmy_page_89 ha scritto:mio dio
è lentissimo e mi causa addirittura problemi in xfce non so come sia possibile ma sembra che xfce non lavori più con dbus
infatti wicd non si avvia più, il vassoio di sistema ora va ora non va e non fa più l'automount
con tutto il rispetto, ma che schifo

jimmy_page_89 ha scritto:mio dio
è lentissimo e mi causa addirittura problemi in xfce non so come sia possibile ma sembra che xfce non lavori più con dbus
infatti wicd non si avvia più, il vassoio di sistema ora va ora non va e non fa più l'automount
con tutto il rispetto, ma che schifo