linux-kernel - Re: [PATCH v11 0/3] printk: Make printk() completely async

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Message-ID: <20160416025529.GA567@swordfish>
Date:	Sat, 16 Apr 2016 11:55:29 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Kara <jack@...e.com>, Petr Mladek <pmladek@...e.com>,
	Tejun Heo <tj@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org,
	Byungchul Park <byungchul.park@....com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v11 0/3] printk: Make printk() completely async

On (04/08/16 02:31), Sergey Senozhatsky wrote:
> Hello,
> 
> This patch set makes printk() completely asynchronous: new messages
> are getting upended to the kernel printk buffer, but instead of 'direct'
> printing the actual print job is performed by a dedicated kthread.
> This has the advantage that printing always happens from a schedulable
> context and thus we don't lockup any particular CPU or even interrupts.

Hello,

Sir, is there anything else you want me to improve in this patch set?

	-ss

> against next-20160407
> 
> v11:
> -- switch default to sync printk
> -- make `synchronous' param RW (Andrew, Jan)
> -- set RT priority to printk kthread (Andrew)
> -- correct comments (Andrew)
> 
> v10:
> -- simplify printk_kthread_need_flush_console (Jan, Petr)
> 
> v9:
> -- move need_flush_console assignment down in vprintk_emit (Jan)
> -- simplify need_flush_console assignment rules (Petr)
> -- clear need_flush_console in printing function (Petr)
> -- rename need_flush_console (Petr)
> 
> v8:
> -- rename kthread printing function (Petr)
> -- clear need_flush_console in console_unlock() under logbuf (Petr)
> 
> v7:
> -- do not set global printk_sync in panic in vrintk_emit() (Petr)
> -- simplify vprintk_emit(). drop some of local variables (Petr)
> -- move handling of LOGLEVEL_SCHED messages back to printk_deferred()
>    so we wake_up_process()/console_trylock() in vprintk_emit() only
>    for !in_sched messages
> 
> v6:
> -- move wake_up_process out of logbuf lock (Jan, Byungchul)
> -- do not disable async printk in recursion handling code.
> -- rebase against next-20160321 (w/NMI patches)
> 
> v5:
> -- make printk.synchronous RO (Petr)
> -- make printing_func() correct and do not use wait_queue (Petr)
> -- do not panic() when can't allocate printing thread (Petr)
> -- do not wake_up_process() only in IRQ, prefer vprintk_emit() (Jan)
> -- move wake_up_klogd_work_func() to a separate patch (Petr)
> -- move wake_up_process() under logbuf lock so printk recursion logic can
>    help us out
> -- switch to sync_print mode if printk recursion occured
> -- drop "printk: Skip messages on oops" patch
> 
> v4:
> -- do not directly wake_up() the printing kthread from vprintk_emit(), need
>    to go via IRQ->wake_up() to avoid sched deadlocks (Jan)
> 
> v3:
> -- use a dedicated kthread for printing instead of using wq (Jan, Tetsuo, Tejun)
> 
> v2:
> - use dedicated printk workqueue with WQ_MEM_RECLAIM bit
> - fallback to system-wide workqueue only if allocation of printk_wq has
>   failed
> - do not use system_wq as a fallback wq. both console_lock() and onsole_unlock()
>   can spend a significant amount of time; so we need to use system_long_wq.
> - rework sync/!sync detection logic
>   a) we can have deferred (in_sched) messages before we allocate printk_wq,
>      so the only way to handle those messages is via IRQ context
>   b) even in printk.synchronous mode, deferred messages must not be printed
>      directly, and should go via IRQ context
>   c) even if we allocated printk_wq and have !sync_printk mode, we must route
>      deferred messages via IRQ context
> - so this adds additional bool flags to vprint_emit() and introduces a new
>   pending bit to `printk_pending'
> - fix build on !PRINTK configs
> 
> 
> Jan Kara (2):
>   printk: Make printk() completely async
>   printk: Make wake_up_klogd_work_func() async
> 
> Sergey Senozhatsky (1):
>   printk: make printk.synchronous param rw
> 
>  Documentation/kernel-parameters.txt |  12 +++
>  kernel/printk/printk.c              | 155 +++++++++++++++++++++++++++++++++---
>  2 files changed, 157 insertions(+), 10 deletions(-)
> 
> -- 
> 2.8.0
>