From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
LKML <linux-kernel@vger.kernel.org>,
akpm@linux-foundation.org, linux-mm@kvack.org,
Cong Wang <xiyou.wangcong@gmail.com>,
Dave Hansen <dave.hansen@intel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
yuwang.yuwang@alibabab-inc.com,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Jan Kara <jack@suse.cz>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
rostedt@rostedt.homelinux.com, kernel-team@lge.com
Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to load balance console writes
Date: Tue, 28 Nov 2017 15:23:26 +0900 [thread overview]
Message-ID: <20171128062326.GA1907@jagdpanzerIV> (raw)
In-Reply-To: <20171127084822.GA15859@X58A-UD3R>
Hi,
On (11/27/17 17:48), Byungchul Park wrote:
[..]
> > + /* Owner will clear console_waiter on hand off */
> > + while (READ_ONCE(console_waiter))
> > + cpu_relax();
> > +
> > + spin_release(&console_owner_dep_map, 1, _THIS_IP_);
> > + printk_safe_exit_irqrestore(flags);
> > +
> > + /*
> > + * The owner passed the console lock to us.
> > + * Since we did not spin on console lock, annotate
> > + * this as a trylock. Otherwise lockdep will
> > + * complain.
> > + */
> > + mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
>
> I'm afraid if it's ok even not to lock(or trylock) actually here. Is there
> any problem if you call console_trylock() instead of mutex_acquire() here?
console_trylock() will not work. console_trylock() implies that the
current printing process does up(), which a) opens a race with possible
console_lock()/console_trylock() from foreign CPUs, and b) additionally
wakes up a task from console_sem wait list [if there was one]. so chances
are some other CPU potentially can acquire the lock ahead of waiter,
forcing the waiter to continue spinning on console_sem. and the bad news
are a) it's spinning with local IRQs disabled and b) that another CPU,
which has acquired the console_sem, can schedule under console_sem.
anyway, we are not going to merge this patch. we already have discussed
that in V3 thread:
https://marc.info/?l=linux-kernel&m=151019815721161&w=2
https://marc.info/?l=linux-kernel&m=151020275921953&w=2
https://marc.info/?l=linux-kernel&m=151020404622181&w=2
https://marc.info/?l=linux-kernel&m=151020565222469&w=2
I took some parts of the Steven's patch set, tho, and backported them
to the current printk_kthread series.
-ss
next prev parent reply other threads:[~2017-11-28 6:23 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-08 15:27 [PATCH v4] printk: Add console owner and waiter logic to load balance console writes Steven Rostedt
2017-11-09 10:12 ` Michal Hocko
2017-11-09 10:22 ` [PATCH v4] printk: Add console owner and waiter logic to loadbalance " Tetsuo Handa
2017-11-09 10:26 ` Michal Hocko
2017-11-09 11:03 ` Tetsuo Handa
2017-11-09 11:31 ` Michal Hocko
2017-11-09 12:07 ` Tetsuo Handa
2017-11-24 15:54 ` [PATCH v4] printk: Add console owner and waiter logic to load balance " Petr Mladek
2017-11-24 15:58 ` Petr Mladek
2017-11-27 8:53 ` Byungchul Park
2017-11-28 1:42 ` Byungchul Park
2017-12-08 14:00 ` Petr Mladek
2017-12-12 5:39 ` Sergey Senozhatsky
2017-12-12 19:27 ` Steven Rostedt
2017-12-13 1:50 ` Sergey Senozhatsky
2017-12-14 14:34 ` Petr Mladek
2017-12-14 13:51 ` Petr Mladek
2017-11-27 8:48 ` Byungchul Park
2017-11-28 6:23 ` Sergey Senozhatsky [this message]
2017-12-22 10:31 ` Petr Mladek
2017-12-22 12:44 ` Steven Rostedt
2018-01-10 12:50 ` Petr Mladek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20171128062326.GA1907@jagdpanzerIV \
--to=sergey.senozhatsky.work@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=byungchul.park@lge.com \
--cc=dave.hansen@intel.com \
--cc=hannes@cmpxchg.org \
--cc=jack@suse.cz \
--cc=kernel-team@lge.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mgorman@suse.de \
--cc=mhocko@kernel.org \
--cc=penguin-kernel@I-love.SAKURA.ne.jp \
--cc=peterz@infradead.org \
--cc=pmladek@suse.com \
--cc=rostedt@goodmis.org \
--cc=rostedt@rostedt.homelinux.com \
--cc=sergey.senozhatsky@gmail.com \
--cc=torvalds@linux-foundation.org \
--cc=vbabka@suse.cz \
--cc=xiyou.wangcong@gmail.com \
--cc=yuwang.yuwang@alibabab-inc.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).