linux-kernel - Re: [PATCH v7 5/5] printk: index: Add indexing support to dev

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Date:   Thu, 17 Jun 2021 12:02:31 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Chris Down <chris@...isdown.name>
Cc:     linux-kernel@...r.kernel.org, Jessica Yu <jeyu@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        John Ogness <john.ogness@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>, kernel-team@...com
Subject: Re: [PATCH v7 5/5] printk: index: Add indexing support to dev_printk

On Tue 2021-06-15 17:52:56, Chris Down wrote:
> While for most kinds of issues we have counters, tracepoints, or metrics
> with a stable interface which can reliably be used to indicate issues,
> in order to react to production issues quickly we sometimes need to work
> with the interface which most kernel developers naturally use when
> developing: printk, and printk-esques like dev_printk.
> 
> dev_printk is by far the most likely custom subsystem printk to benefit
> from the printk indexing infrastructure, since niche device issues
> brought about by production changes, firmware upgrades, and the like are
> one of the most common things that we need printk infrastructure's
> assistance to monitor.
> 
> Often these errors were never expected to practically manifest in
> reality, and exhibit in code without extensive (or any) metrics present.
> As such, there are typically very few options for issue detection
> available to those with large fleets at the time the incident happens,
> and we thus benefit strongly from monitoring netconsole in these
> instances.
> 
> As such, add the infrastructure for dev_printk to be indexed in the
> printk index. Even on a minimal kernel config, the coverage of the base
> kernel's printk index is significantly improved:
> 
> Before:
> 
>     [root@...t ~]# wc -l /sys/kernel/debug/printk/index/vmlinux
>     4497 /sys/kernel/debug/printk/index/vmlinux
> 
> After:
> 
>     [root@...t ~]# wc -l /sys/kernel/debug/printk/index/vmlinux
>     5573 /sys/kernel/debug/printk/index/vmlinux
> 
> In terms of implementation, in order to trivially disambiguate them,
> dev_printk is now a macro which wraps _dev_printk.
> 
> Signed-off-by: Chris Down <chris@...isdown.name>

Reviewed-by: Petr Mladek <pmladek@...e.com>
Tested-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr