On Wed, Jan 4, 2017 at 4:02 PM, Eswaran Vinothkumar (BEG-PT/PJ-IOT1) < vinothkumar.eswa...@de.bosch.com> wrote:
> Hello systemd developers, > > > > Currently, I am working on a task to reduce the boot time of an embedded > product. systemd is used as the init system. I have a couple of questions, > could you please clarify? > > > > 1. From the systemd-analyze plot, I am seeing that it takes around 2 > seconds to load the systemd unit files. Is there any way to reduce this > time? I read a blog about systemd-readahead and systemd-replay services > used in such cases to reduce the loading time, but it also have mentioned > that the services are not maintained in the latest systemd versions. Is it > advisable to use such services? > There still are other readahead implementations, although I doubt they'll help at all if you're reading from flash memory... also, they usually run as regular early services, after all units have loaded. In fact, if something like *unit loading* is slow, you might have other problems... Use systemd-bootchart or other similar tools to figure out whether the loading is I/O-bound or CPU-bound. It could also be that some *unit generators* take a long time to run – consider masking or outright deleting some of them. > 2. There are some systemd services which are used mostly for debugging > purposes, so I tried to mask those services. My question is if the service > is masked , do the service files gets loaded during the systemd > initialization? I have masked around 5 services but I am not seeing any > reduction in the systemd unit files loading time though there is a > considerable reduction in the overall boot time. > AFAIK, no; systemd stops looking after it finds the first matching unit. You could also remove the unneeded unit files entirely and compare the results. (But see reply to #1 first.) > 3. I have read that the preferred way to have the mount points is > to write in /etc/fstab. This will create a *.mount file using > systemd_fstab_generator. I am seeing that in the project for the debugfs > there is a systemd mount file defined in /lib/systemd/system/ and also an > option present in /etc/fstab (‘*debugfs /sys/kernel/debug debugfs > noauto 0 0’).* > On embedded systems, where you make your own rules, I'd say creating your own mount units would be more direct and easier to debug – also possibly avoiding a slow generator call. (Though, on the other hand, some filesystems are mounted by src/core/mount-setup.c before processing any units. Later on, systemd-remount-fs applies options from fstab but not from custom .mount units...) Which file has precedence when the system is initialized? > > > > /lib/systemd/system/sys-kernel-debug.mount > > or > > /run/systemd/generator/sys-kernel-debug.mount > > fstab takes priority over packaged .mount units – it's one of the ways sysadmins can override systemd default mount options. The (mostly) full order is: * /run/systemd/system * /run/systemd/generator.early * /etc/systemd/system * /run/systemd/system * /run/systemd/generator * /usr/lib/systemd/system * /lib/systemd/system * /run/systemd/generator.late See src/shared/path-lookup.c for the full (not-quite-documented) details. -- Mantas Mikulėnas <graw...@gmail.com>
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