Messages in this thread | | | Date | Sat, 21 May 2022 20:51:54 +0200 | From | Greg Kroah-Hartman <> | Subject | Re: [RFC PATCH v2] printk: console: Allow each console to have its own loglevel |
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On Fri, May 20, 2022 at 01:57:19PM +0100, Chris Down wrote: > [Once the goals of this patch are generally agreed upon, it can be split > out further with more detailed changelogs if desired.] > > Consoles can have vastly different latencies and throughputs. For > example, writing a message to the serial console can take on the order > of tens of milliseconds to get the UART to successfully write a message. > While this might be fine for a single, one-off message, this can cause > significant application-level stalls in situations where the kernel > writes large amounts of information to the console. > > This means that while you might want to send at least INFO level > messages to (for example) netconsole, which is relatively fast, you may > only want to send at least WARN level messages to the serial console. > Such an implementation would permit debugging using the serial console > in cases that netconsole doesn't receive messages during particularly > bad system issues, while still keeping the noise low enough to avoid > inducing latency in userspace applications. This patch adds such an > interface, extending the existing console loglevel controls to allow > each console to have its own loglevel. > > One can't just disable the serial console, because one may actually need > it in situations where the machine is in a bad enough state that nothing > is received on netconsole. One also can't just bump the loglevel at > runtime after the issue, because usually the machine is already so > wedged by this point that it isn't responsive to such requests. > > In terms of technical implementation, this patch embeds a device pointer > in the console struct, and registers each console using it so we can > expose attributes in sysfs. > > The lifecycle of this classdev looks like this on registration: > > register_console(con)/printk_late_init() > console_register_device(con) > device_initialize(con->classdev) # refcount++ > device_add(con->classdev) # refcount++ > > At stable state, the refcount is two. > > Console unregistration looks like this: > > [con->classdev refcount drops to 0] > console_classdev_release(con->classdev) > kfree(con->classdev) > > unregister_console(con) > device_unregister(con->classdev) > device_del(con->classdev) # refcount-- > device_remove_class_symlinks() > kernfs_remove_by_name_ns() > kernfs_drain() > kernfs_drain_open_files() # wait for close() > put_device(con->classdev) # refcount-- > > We also deprecate the kernel.printk sysctl as it doesn't know about > per-console loglevels, and is generally pretty confusing. > > For information on the precedence and application of the new controls, > see Documentation/ABI/testing/sysfs-class-console and > Documentation/admin-guide/per-console-loglevel.rst. > > Signed-off-by: Chris Down <chris@chrisdown.name> > --- > Documentation/ABI/testing/sysfs-class-console | 50 +++ > .../admin-guide/kernel-parameters.txt | 18 +- > .../admin-guide/per-console-loglevel.rst | 116 ++++++ > Documentation/admin-guide/serial-console.rst | 17 +- > Documentation/core-api/printk-basics.rst | 34 +- > Documentation/networking/netconsole.rst | 17 + > MAINTAINERS | 3 + > include/linux/console.h | 23 ++ > include/linux/kern_levels.h | 2 + > init/main.c | 2 +- > kernel/printk/console_cmdline.h | 2 + > kernel/printk/printk.c | 352 ++++++++++++++++-- > kernel/printk/sysctl.c | 95 ++++- > 13 files changed, 680 insertions(+), 51 deletions(-) > create mode 100644 Documentation/ABI/testing/sysfs-class-console > create mode 100644 Documentation/admin-guide/per-console-loglevel.rst
You forgot what changed from v1 :(
Anyway, the driver model interaction looks good to me, nice work, no objections at all.
gre gk-h
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